Aims In contrast to temperate regions,the reasons for growth reductions of individual tree species along elevational gradients in tropical mountain ranges are poorly known,especially for tropical conifers.We aimed at ...Aims In contrast to temperate regions,the reasons for growth reductions of individual tree species along elevational gradients in tropical mountain ranges are poorly known,especially for tropical conifers.We aimed at testing whether climatic or edaphic conditions are responsible for the reduced growth of Pinus kesiya,a widely distributed pine species of southern and south-eastern Asia,at higher elevations.Methods We analysed the stem diameter increment and the isotope discrimination against ^(13)C(△^(13)C)in tree rings of P.kesiya along an elevational gradient of~900 to~2000 m a.s.l.in the mountain ranges of South-Central Vietnam,and related growth to△^(13)C and to climatic and edaphic variables.Important findings We found no consistent correlation patterns between the basal area increment(BAI)of the trees and temperature or precipitation.In contrast,across the elevational gradient,we obtained significantly negative correlations of BAI with△^(13)C and with the C/N ratios and theδ^(15)N signature of the upper mineral soil.BAI was positively correlated with the concentrations of plant-available phosphorus(P_(a))and of“base”cations(calcium,magnesium,potassium)in the soil.We conclude that lower temperatures at higher elevations exert an indirect effect on tree growth by inducing higher C/N ratios and by reducing the rate of nitrogen(N)and P mineralization,which may be further hampered by lower concentrations of“base”cations(upon enhanced leaching by precipitation)and a negative feedback from low availability of mineralized N and P at higher elevations.Our results may be transferable to the uppermost growth limit of P.kesiya and to other montane regions of the species’occurrence.展开更多
Species＇ partitioning of resources remains one of the most integral components for understanding community assem- bly. Analysis of stable carbon and nitrogen isotopes in animal tissues has the potential to help resol...Species＇ partitioning of resources remains one of the most integral components for understanding community assem- bly. Analysis of stable carbon and nitrogen isotopes in animal tissues has the potential to help resolve patterns of partitioning be- cause these proxies represent the individual＇s diet and trophic niche, respectively. Using free-ranging rodents in a southern Afri- can savanna as a model community, we find that syntopic species within habitats occupy distinct isotope niches. Moreover, spe- cies with strongly overlapping isotope niches did not overlap in their spatial distribution patterns, suggesting an underlying effect of competitive exclusion. Niche conservatism appears to characterize the behaviour of most species in our sample - with little or no observed changes across habitats - with the exception of one species, Mastomys coucha. This species displayed a generalist distribution, being found in similar abundances across a variety of habitats. This spatial pattern was coupled with a generalist isotope niche that shifted across habitats, likely in response to changes in species composition over the same spatial gradient. The case for M. coucha supports contentions that past competition effects played a significant evolutionary role in shaping community structures of today, including the absence of strong interspecific niche overlaps within particular habitats. Our study highlights the value of stable isotope approaches to help resolve key questions in community ecology, and moreover introduces novel ana- lytical approaches to quantifying isotope niche breadths and niche overlaps that are easily comparable with traditional metrices展开更多
基金supported by the State of Vietnam through a PhD grant to L.T.H.(Grant No.4358/QĐ-BGDĐT)by the Deutscher Akadamischer Austauschdienst(DAADProject No.57163751)through covering travel costs of R.S.and F.M.T.
文摘Aims In contrast to temperate regions,the reasons for growth reductions of individual tree species along elevational gradients in tropical mountain ranges are poorly known,especially for tropical conifers.We aimed at testing whether climatic or edaphic conditions are responsible for the reduced growth of Pinus kesiya,a widely distributed pine species of southern and south-eastern Asia,at higher elevations.Methods We analysed the stem diameter increment and the isotope discrimination against ^(13)C(△^(13)C)in tree rings of P.kesiya along an elevational gradient of~900 to~2000 m a.s.l.in the mountain ranges of South-Central Vietnam,and related growth to△^(13)C and to climatic and edaphic variables.Important findings We found no consistent correlation patterns between the basal area increment(BAI)of the trees and temperature or precipitation.In contrast,across the elevational gradient,we obtained significantly negative correlations of BAI with△^(13)C and with the C/N ratios and theδ^(15)N signature of the upper mineral soil.BAI was positively correlated with the concentrations of plant-available phosphorus(P_(a))and of“base”cations(calcium,magnesium,potassium)in the soil.We conclude that lower temperatures at higher elevations exert an indirect effect on tree growth by inducing higher C/N ratios and by reducing the rate of nitrogen(N)and P mineralization,which may be further hampered by lower concentrations of“base”cations(upon enhanced leaching by precipitation)and a negative feedback from low availability of mineralized N and P at higher elevations.Our results may be transferable to the uppermost growth limit of P.kesiya and to other montane regions of the species’occurrence.
基金Acknowledgements This research was funded by the Na- tional Science Foundation （NSF, USA） and the Palaeontolo- gical Scientific Trust （PAST, RSA）. We thank Jurie du Plessis, Isak Sekhuni, Carl Pohl, Bianca Bester, Ethan Codron, and Jesse Codron for assistance in the field. Two anonymous re- viewers and the journal editor are thanked for useful com- ments that helped improve the quality of this paper. The re- search and protocols were approved by the Gauteng Provincial Government, authorization number MA： 8/1/1/6/1-2011/01/001.
文摘Species＇ partitioning of resources remains one of the most integral components for understanding community assem- bly. Analysis of stable carbon and nitrogen isotopes in animal tissues has the potential to help resolve patterns of partitioning be- cause these proxies represent the individual＇s diet and trophic niche, respectively. Using free-ranging rodents in a southern Afri- can savanna as a model community, we find that syntopic species within habitats occupy distinct isotope niches. Moreover, spe- cies with strongly overlapping isotope niches did not overlap in their spatial distribution patterns, suggesting an underlying effect of competitive exclusion. Niche conservatism appears to characterize the behaviour of most species in our sample - with little or no observed changes across habitats - with the exception of one species, Mastomys coucha. This species displayed a generalist distribution, being found in similar abundances across a variety of habitats. This spatial pattern was coupled with a generalist isotope niche that shifted across habitats, likely in response to changes in species composition over the same spatial gradient. The case for M. coucha supports contentions that past competition effects played a significant evolutionary role in shaping community structures of today, including the absence of strong interspecific niche overlaps within particular habitats. Our study highlights the value of stable isotope approaches to help resolve key questions in community ecology, and moreover introduces novel ana- lytical approaches to quantifying isotope niche breadths and niche overlaps that are easily comparable with traditional metrices
