Báo cáo khoa học: "The decline of a Pinus nigra Arn. reforestation stand on a limestone substrate: the role of nutritional factors examined by means of foliar diagnosis"

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Original article The decline of a Pinus nigra Arn. reforestation stand on a limestone substrate: the role of nutritional factors examined by means of foliar diagnosis Enrico Cenni, Filippo Bussotti Lorenzo Galeotti Laboratory of Applied and Forest Botany, Department of Plant Biology, University of Florence, Piazzale delle Cascine 28, I 50144 Florence, Italy (Received 6 June 1997; accepted 26 November 1997) Abstract - The Austrian black pine reforestation projects on Monte Morello, near the heavily pop- ulated metropolitan area of Florence (Italy), have been affected for many years now by a severe decline consisting of widespread crown yellowing. To investigate the causes of this decline foliar diagnosis methods were used to monitor the nutritional status of ten trees, sampling and analysing every year, between 1989 and 1992, the current year needles (c), needles from the previous year (c+ I) and from the year before that (c+2). The parameters examined were both chem- ical (nitrogen, sulphur, magnesium, potassium, calcium, manganese, iron and lead) and mor- phological (needle length, flat projection, dry weight, specific dry weight and water content). The findings show a considerable calcium accumulation as the needles age, accompanied by an increase in dry weight and specific dry weight, as well as a marked antagonism to manganese. The influence of the nearby metropolitan area of Florence is suggested by the accumulation of lead. (© Inra/Elsevier, Paris) afforestation / calcium / iron / leaf / manganese / Pinus / nigra subsp. nigra senescence chlorosis Résumé - Le dépérissement des reboisements de Pinus nigra Arn. sur substrat calcaire ; le rôle des facteurs nutritionnels étudiés à l’aide du diagnostic foliaire. Les reboisements de pin noir d’Autriche dans le Monte Morello, près de l’importante zone urbaine de Florence (Italie) sont affectés depuis maintenant plusieurs années d’un sévère dépérissement consistant en un jaunis- sement très fréquent des couronnes. Pour étudier les causes de ce dépérissement, des méthodes d’analyse foliaire ont été utilisées pour suivre l’état nutritionnel de dix arbres échantillonnés et analysés chaque année entre 1989 et 1992, en prenant en compte les aiguilles de l’année (c), les aiguilles de l’année précédente (c+1) et les aiguilles âgées de 2 ans (c+2). Les paramètres étudiés étaient chimiques (azote, soufre, magnésium, potassium, calcium, manganèse, fer, plomb) mor- * Correspondence and reprints E-mail: fbussotti@cesitl.unifi.it
phologiques (longueur des aiguilles, surface projetée, poids sec spécifique et teneur en eau). Les résultats montrent une accumulation considérable de calcium avec l’âge des aiguilles accompa- gnée par un accroissement du poids sec et du poids spécifique, ainsi qu’un antagonisme marqué du manganèse. L’influence de l’agglomération voisine de Florence est suggérée par l’accumulation de plomb. (© Inra/Elsevier, Paris) reboisement / calcium / fer / sénescence foliaire / manganèse / Pinus nigra subsp. Nigra / chlorose located in 1. INTRODUCTION urbanized densely they are a (more than1 million inhabitants). area Thus, any conclusions drawn as to their In the first half of this century, several ecological stability or instability could be species of conifers were widely used in a valid contribution in guiding the deci- Italy to reforest areas where the sions of the city’s administrators on the autochthonous forest vegetation normally fate and management of these stands. consists of broadleaved trees. The purpose of these reforestation projects was usually either timber production or hydrogeolog- ical protection. Pinus nigra Am., with all 2. MATERIALS AND METHODS its various subspecies, thanks to its remarkable ecological flexibility, was one 2.1. Study area of the species most widely used. Today the forest landscape of many Italian Monte Morello is a mountain ridge (maxi- regions is characterized by the presence height: 934 m a.s.l.) running from NW to mum of stretches of conifer forests surrounded SE, located immediately north-west of the urban area of Florence. The prevailing litho- by broadleaf woods with no apparent land- logical component is limestone and marl; the scape and/or ecological continuity. If we forest soils are for the most part shallow, rich further consider that these species were in skeleton and scarse in humified organic sub- often planted in environments that were stances. The mean pH of the surface layer of very far from their ecologically ideal set- the soil (0-20 cm) is 7.76; the CaCO content 3 ting, and that they are showing all the signs ranges from 10 % in the upper layer (0-5 cm under the organic matter layer) to 30 % (at of premature senescence and ecological 10-20 cm deep). The climate is temperate, with instability, it is easy to understand how in hot summers characterized by moderately recent years a lot of discussion has been severe droughts; the mean yearly temperature devoted to the topic, especially the need to is about 12 °C, while mean yearly rainfall allow the sites to gradually revert to a more ranges from 900 mm at the lower altitudes to natural vegetation [24]. 1 100-1 200 mm at the higher ones. Monte Morello marks the transition point between a In the light of this, our paper examines thermophile sub-Mediterranean flora and a artificial Pinus nigra stands growing on mountain flora typical of the Apennines. Most Monte Morello, in a peri-urban environ- of the spontaneous stands consist of mixed ment near the metropolitan area of Flo- deciduous xerothermal oakwoods, typical of rence (Tuscany, central Italy), and show- the sub-Mediterranean horizon, with a preva- lence of Quercus pubescens Willd. and Frax- ing severe crown yellowing. The purpose inus ornus L. Anthropogenous vegetation is of this study is to assess the vegetational also very widespread, for the most part con- conditions by means of foliar diagnostics sisting of conifer reforestation projects, grow- [2, 4]. These artificial stands, planted for ing mainly at the higher altitudes of the moun- protective purposes, today still have an tain ridge, but also present along the southern important recreational function, in that slopes of the lower hillsides. These stands are
ascribed to the poor stand conditions and an made up of conifers, the result of planting pro- grammes [26] begun in 1909 and continued, insufficient mycorrhizal status. This symp- with diminishing intensity, till the early 1970s. tomatology is still evident today. The purpose of all these planting programmes was to provide hydrogeological stability in areas with difficult pedoclimatic conditions 2.2. Sampling which were covered by secondary meadows or by degraded broadleaf woods. Today, the artificial stands cover an area greater than 500 The study examined ten Austrian pines, ha. The most widely used species are Austrian between 50 and 70 years old, two from each pine and laricio pine (Pinus nigra subsp. nigra of five stands along the main ridge of the and Pinus nigra subsp. laricio (Poiret) Maire), mountain. Needles from the upper third of the cypress (Cupressus sempervirens L.) and silver crown were sampled from each tree: needles fir (Abies alba Mill.), with a sporadic presence that had sprouted during the sampling year (c, of other species. These stands are often char- needles that were about 4 months old at the acterized by poor regeneration, marked sus- time of sampling), needles from the previous ceptibility to adversities and a high degree of year (c+1, needles aged about 16 months) and inflammability. Moreover, the soil they grow from the year before that (c+2, needles aged on, despite the satisfactory evolution under- about 28 months). Samples were collected for gone as compared to the pre-existing situation four consecutive years, from 1989 to 1992, [3], is still poorly evolved and fairly shallow. always at the end of summer and following the Black pines were used also at lower altitudes, UN-ECE guidelines [28]. Table I illustrates and in conditions that are definitely more the sampling protocol. Mediterranean than the ecological requirements of the species [14]. The reforestation projects on Monte Morello 2.3. Chemical and morphological tests among the first stands studied in Italy for were the decline of black pines caused by unknown agents [5] and the influence of air pollutants Nitrogen, sulphur, calcium, magnesium, was hypothesized. In fact the influence of the potassium, manganese, iron and lead levels metropolitan area is notable primarily in the were determined. Nitrogen and sulphur levels marked acidification of the precipitations [1, measured with a CHNS Element Ana- were 13] and in the high summertime concentra- Erba mod. EA 1108). Analytical lyzer (Carlo tions of ozone (Italian Botanical Society, determination of the remaining elements (total unpublished report). Thanks to the limestone quantities) was carried out after wet digestion matrix of the soil, however, no phenomena of in HNO (Suprapur Merck) with depositing 3 soil acidification have been observed [30]. refrigeration with an atomic absorption spec- Moreover, as early as the 1970s, Poggesi trophotometer (Varian Spectra AA-20): cal- cium, iron, potassium, magnesium, manganese, [26] was already reporting widespread occur- with flame atomization; lead in a graphite oven. of needle in black yellowing pines, rences
the other hand, reports the chemical The following morphological parameters on of 100 needles were also assessed: the flat pro- and morphological differences between jection (Area), using a Licor LI-3100 area needles of different ages: the variance meter; their fresh weight (FW) and, after dry- analysis allows us to establish that the ing in an oven at 60 °C till they reached a con- majority of parameters (except needle stant weight, their dry weight (DW). The fol- length and the surface of the flat projection lowing parameters were then calculated: water 1 - (DW/FW)100) and specific content (WC among the morphological parameters, and = dry weight (SDW DW/Area). = magnesium concentration among the All data are expressed as mean values, stan- chemical ones) displays a gradient in cor- dard deviation and correlations; a variance relation to the needle’s age: dry weight, analysis with ANOVA-LSD test and discrim- specific dry weight and concentrations of inant analysis were further performed. The calcium, iron and lead all increase their software used was Statistica Statsoft Inc. and levels as the needles grow older, while the SPSS for Windows 6.0. other parameters all diminish. The correlation between morphologi- 3. RESULTS cal and chemical parameters were calcu- lated separately for the needles of the dif- The data in table II show the yearly ferent ages (c, c+1, c+2) and then globally, variations in the nutritional status and mor- for the entire sample, using Spearman’s phology of the needles over the entire non-parametric r coefficient. The signifi- period of the study. The variance analy- cant correlations which are of the great- sis results (ANOVA-LSD test) show that est interest within the context of this inves- the values fluctuate considerably, espe- cially the chemical parameters. Table III, tigation are described in detail below: they
relate primarily to the levels of calcium, 3.2. c+1 and c+2 needles iron and manganese. In c+1 needles, and even more so in c+2 needles, most of the correlations found in c needles are no longer observable. Yet, 3.1. needles c in c+1 needles the iron-manganese-cal- cium group behaves in a very similar man- ner to how it behaves in c needles, while Iron and manganese correlate inversely these correlations are no longer there in calcium (iron-calcium: no. 40, r to = c+2 needles. P - 0.34, 0.0276; manganese-calcium: = -0.53, P 0.00041) and both no. 40, r = = elements correlate positively to each other 3.3. Needles of all ages (no. 40, r 0.59, P 0.00005). These = = trends are visualized in figures 1 and 2. In order to have an equal representa- Figure 1 also shows that the calcium-man- tion of all ages examined, only the data ganese and calcium-iron relations are bet- from the samplings of 1991 and 1992 were ter expressed by logarithmic-type func- processed and included in the calculations tions than by linear ones. Considering the (i.e. the values for 60 cases, distributed as dry weight of 100 needles as a parameter follows: 20 c needles, 20 c+1 and 20 c+2). of productivity, one can observe that it The correlations described above hold true correlates inversely with both iron (no. for the entire sample, except for the cor- 30, r -0.51, P 0.0036) and manganese relation between calcium and iron which is = = no longer visible. In this context it is inter- (no. 30, r = -0.45, P 0.0105). =
ing between the different needle ages: cal- esting to note that some elements fre- quently accompany the ageing processes cium, iron and manganese. Calcium (which has the lowest Wilks lambda) con- which are expressed through a change in specific dry weight (it increases) and/or tributes more than any other variable to the total discrimination of the three groups; water content (it decreases). Calcium cor- relates strongly with both these parameters manganese and iron follow in decreasing order. Of the two extracted canonic func- (no. 60, Ca-WC: r=-0.58, P < 0.001; Ca- SDW: r 0.38, P = 0.0062), whereas iron tions only the first is significant (98 % of = only with specific dry weight the discriminating power is provided by correlates 0.0092). These find- this function): it distinguishes between 0.37, P (no. 60, r = = group 1 (c needles) and group 3 (c+2 nee- also reported in figures3 and 4, ings are where we can observe that these correla- dles), where the difference between the mean values is greatest. Of the three vari- tions are expressed better by exponential- type functions. ables, iron is the one that contributes most to the discrimination specified by this Lastly, a discriminant analysis was per- function. formed in order to ascertain the relative weight of each variable considered in the differentiation of the three needle ages. In 4. DISCUSSION order to select those variables that are important in distinguishing the groups, a The findings on the nutritional status stepwise selection algorithm was used: the results are summarized in table IV. There of Austrian pine needles, if compared to are three elements capable of distinguish- the nutrional standards of this species or
similar species (cf. [2, 4, 19, 29]), mainly iron levels, and these elements (iron in c show a considerable accumulation of cal- needles, but mainly manganese) are clearly deficient. cium that is more evident in c+1and c+2 needles. The increase in calcium in the Sulphur levels are also very low, but older needles is a well-known physiolog- the concentration of this element is com- ical phenomenon [11], although in this parable to the mean values measured in case it has undoubtedly been accentuated Italy in a number of forest species [7, 23]; by the geological matrix. According to the low and diminishing levels of sulphur Bergmann [2] iron and manganese also allow us to rule out any significant impact accumulate in the older needles, but in our of SO from the surrounding urbanized 2 findings this can only be observed in the areas. Rather, the impact of the metropoli-
tan area nearby is detectable with the cium plays a decisive role, influencing high lead concentration levels. both the absorption and metabolism of several microelements (iron and - even Magnesium is constantly maintained more so - manganese) and the processes optimum levels, in accordance with at of foliar ageing. As the needle ages, cal- other observations of this element on lime- cium probably accumulates in the form of stone soils [2], whereas on acid soils there oxalate crystals both inside the vacuoles are often incidences of chlorosis due to and in the apoplast, as well as in extracel- magnesium deficiency [18]. Potassium lular sites [11, 12]. These processes prob- concentrations are close to ideal levels in ably also cause the increase in dry weight. c needles, but they decrease considerably The findings of this study allow us to con- in older needles. Low levels of potassium clude that calcium can be considered as are usual in trees growing on limestone ’the independent ecological variable’ soils [2]. An analogous behaviour of potas- which exercises a dominant role over all sium concentrations has been described the chemical and morphological parame- by Magalotti et al. [23] in Pinus pinea L. ters. needles growing on terrain characterized by sodium alkalinity. It is interesting to observe the differ- behaviour patterns of calcium, man- ent The decrease in concentration of some ganese and iron in relation to the senes- elements is a normal feature related to the cence process. The needle’s ageing may ageing process [20]. According to Schulze be expressed by means of an increase in [27] conifers subjected to stress translo- specific dry weight. While calcium and cate part of their nutritional elements from iron display an exponential-type positive the older needles to the younger ones. correlation with specific dry weight (fig- The morphological changes observed ures 3 and 4), this does not occur with in this study (increased specific dry weight manganese (figure 4). These findings sug- and reduced water content), although they gest that calcium exerts a greater antago- have already been observed in other nistic action on manganese than on iron. species before, are consistent with pro- The former no longer cumulates in the cesses of stress and/or ageing [7, 8]. needles after the first year of their life, Potassium, iron and manganese defi- whereas the uptake and storage of the lat- ciencies have been reported as inducing ter is continuous. needle chlorosis in trees growing mainly on limestone soils [2, 17, 21, 27]. On lime- stone soil, in fact, calcium exerts an antag- 5. CONCLUSIONS onistic action towards these elements, especially against iron and manganese [2]. The findings described above suggest Sulphur deficiencies can also be consid- that the poor conditions of the Pinus nigra ered as a factor predisposing the tree to reforestation site on Monte Morello can chlorosis [10, 21]. be related to nutritional deficiencies and Especially noteworthy is the wide range inbalances, despite the fact that this species of fluctuations between one year and the is normally assumed to be sparing and tol- next. In the 1990 sampling a higher level erant to calcium and environmental stress of manganese and iron was detected, but factors. In fact in the study stand the trees no evaluable changes in crown conditions are growing in extreme conditions, on a were observed. rocky limestone soil outside their ideal An analysis of the correlations between climate range. Our findings show that the parameters examined suggests that cal- there is a considerable antagonism
between calcium and manganese, and that quence, of their ability to perform the func- a manganese deficiency (combined with a tions they were designed for. less marked iron deficiency) can cause extensive leaf yellowing, a symptom described as ’limestone chlorosis’ (cf. ACKNOWLEDGEMENTS [16]). The low levels of potassium and This study was carried out thanks to a con- sulphur may contribute to chlorosis. tribution by the Regione Toscana (Study on Hilbrunner and Flückiger [17] have forest damage). The Authors wish to thank Mr reported on several Abies alba Mill. refor- Giulio Boschi for the sampling; Agrochimica estation stands with marked instances of Pisana for the chemical analyses and Dr Piero chlorosis due to manganese deficiency. In Bruschi for assistance with the statistics. such conditions needle chlorosis induced by manganese deficiency is frequently more pronounced in current-year needles REFERENCES than in older needles. Bellandi S., Cenni E., Gellini R., Ferretti M., [1] The fact that yearly fluctuations in the Pantani F., Veneziani M., Chimismo delle mineral content of the needles are not precipitazioni in una foresta periurbana dell’area fiorentina, Acqua Aria (10) (1993) immediately reflected by significant 1095-1100. changes in crown conditions suggests that Bergmann W., Nutritional Disorder of Plants, [2] the relationships among the elements are G. Fisher Verlag, Jena, 1992. complex and their balance plays a funda- Bernetti G., Osservazioni sull’influenza della [3] mental role [27], as well as the relation- sul terreno nei rimboschimenti vegetazione di Monte Morello, in: Atti del congresso ships among elements, other environ- nazionale sui rimboschimenti e sulla ricosti- mental factors and the physiological tuzione dei boschi degradati, vol. II, Firenze, functions of the trees. 1961, pp. 99-110. Bonneau M., La diagnostic foliaire, Rev. For. [4] The Monte Morello forest is very close Fr. 40 (1988) 19-28. to a highly urbanized environment and is Bottacci A., Brogi L., Bussotti F., Cenni E., [5] affected by pollutants originating from Clauser F., Ferretti M., Gellini R., Grossoni that area (acid rains and ozone): that may P., Schiff S., Inquinamento ambientale e deperimento del bosco in Toscana, Regione also be important, but we still do not know Toscana, Società Botanica Italiana, Firenze, exactly how this factor interacts with the 1988. edaphic and nutritional stresses described Bussotti F., Ferretti M., Cenni E., Gellini R., [6] above. Clauser F., Grossoni P., Barbolani E., New type forest damage to mediterranean vegeta- From a more general point of view, this tion in Southern Sardinian forests (Italy), Eur. study offers a further contribution to the J. For. Path. 21 (1991) 290-300. issues relating to the decline of artificial Bussotti F., Ferretti M., Cenni E., Grossoni P., [7] Monitoring of mineral nutrients and trace ele- coniferous reforestation sites (cf. [6, 9, 15, ments in broadleaves: a survey in Tuscany, in: 17, 22, 25]), especially when the ecologi- Nilsson L.O., Hüttl R.F., Johansson U.T., cal compatibility between species and Mathy P. (Eds.), Nutrient Cycling in Forest stand is not ideal. It is highly likely that Ecosystems, Proc. CEC/IUFRO Sym- posyum,. Ecosystem Res. Rep., Brussels 21 this type of difficulty will increase in the (1995) 99-106. future, owing to possible climate changes. Bussotti F., Grossoni P., Bottacci A., Scle- [8] Thus, the study of naturalistic criteria to be rophylly in beech (Fagus sylvatica L.) trees: followed in reforestation projects becomes its relationship with crown transparency, nutritional status and summer drought, a necessity not merely from the aesthetic Forestry 70 (1997) 267-271. and landscape-planning point of view, but P., Indagine sui danni da gelo nelle Cantiani [9] also as a guarantee of the ecological sta- pinete dell’alto litorale adriatico, It. For. Mont. bility of the plantations and, as a conse- 1 (1994) 54-70.
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