Um estudo [Recent widespread tree growth decline despite increasing atmospheric CO2] publicado na PLoS ONE da semana passada indica que, em vez de crescer mais rapidamente e absorver mais dióxido de carbono, na medida em que o planeta se aquece, as árvores da floresta pode crescer mais lentamente. Mais dióxido de carbono na atmosfera geralmente deve aumentar as taxas de crescimento das plantas, uma vez que o dióxido de carbono é a matéria-prima para a fotossíntese. Pelo menos em tese.

Por outro lado, a elevação das temperaturas pode colocar as plantas sob estresse, o que pode compensar os benefícios de mais dióxido de carbono.

Os pesquisadores examinaram amostras de núcleo de quatro espécies de árvore [abeto-negro, pinheiro vermelho, carvalho vermelho e bordo], cujo crescimento, nas florestas de Ontário, é bem documentado. A partir dos exames, os pesquisadores descobriram que os anéis de crescimento das árvores foram mais estreitos nos anos mais recentes, com o dióxido de carbono atmosférico aumentado.

A comparação dos anéis de crescimento com as taxas de isótopos de carbono (que captam a resposta de uma árvore ao estresse de temperatura) sugeriram que o declínio do crescimento foi devido a temperaturas menos ‘hospitaleiras’. O aumento da temperatura, portanto, foi mais do que suficiente para compensar o aumento do dióxido de carbono, reduzindo a taxa de crescimento.

Para acessar o artigo ‘Recent widespread tree growth decline despite increasing atmospheric CO2‘, na íntegra e no formato HTML, clique aqui. Abaixo, para maiores informações, transcrevemos o abstract.

Silva, L., Anand, M., & Leithead, M. (2010). Recent widespread tree growth decline despite increasing atmospheric CO2. PLoS ONE, 5 (7) DOI: 10.1371/journal.pone.0011543

Recent Widespread Tree Growth Decline Despite Increasing Atmospheric CO2

Abstract

Background
The synergetic effects of recent rising atmospheric CO2 and temperature are expected to favor tree growth in boreal and temperate forests. However, recent dendrochronological studies have shown site-specific unprecedented growth enhancements or declines. The question of whether either of these trends is caused by changes in the atmosphere remains unanswered because dendrochronology alone has not been able to clarify the physiological basis of such trends.

Methodology/Principal Findings
Here we combined standard dendrochronological methods with carbon isotopic analysis to investigate whether atmospheric changes enhanced water use efficiency (WUE) and growth of two deciduous and two coniferous tree species along a 9° latitudinal gradient across temperate and boreal forests in Ontario, Canada. Our results show that although trees have had around 53% increases in WUE over the past century, growth decline (measured as a decrease in basal area increment – BAI) has been the prevalent response in recent decades irrespective of species identity and latitude. Since the 1950s, tree BAI was predominantly negatively correlated with warmer climates and/or positively correlated with precipitation, suggesting warming induced water stress. However, where growth declines were not explained by climate, WUE and BAI were linearly and positively correlated, showing that declines are not always attributable to warming induced stress and additional stressors may exist.

Conclusions
Our results show an unexpected widespread tree growth decline in temperate and boreal forests due to warming induced stress but are also suggestive of additional stressors. Rising atmospheric CO2 levels during the past century resulted in consistent increases in water use efficiency, but this did not prevent growth decline. These findings challenge current predictions of increasing terrestrial carbon stocks under climate change scenarios.

Citation: Silva LCR, Anand M, Leithead MD (2010) Recent Widespread Tree Growth Decline Despite Increasing Atmospheric CO2. PLoS ONE 5(7): e11543. doi:10.1371/journal.pone.0011543

Editor: Tamara Natasha Romanuk, Dalhousie University, Canada

Received: April 23, 2010; Accepted: June 8, 2010; Published: July 21, 2010

Copyright: © 2010 Silva et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: This work was funded by Inter-American Institute for Global Change Research, the Natural Sciences and Engineering Council of Canada, the Canadian Foundation for Innovation, and the University of Guelph grants to M.A. who holds the Canada Research Chair in Global Ecological Change. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

* E-mail: manand@uoguelph.ca

(Por Henrique Cortez, do EcoDebate, 20/08/2010)