氮沉降对森林植物的影响

Impact of nitrogen deposition on forest plants

综述了氮沉降对森林植物的影响。氮沉降对森林植物的影响主要表现在以下6个方面:(1)在一定量范围内的氮沉降有利于植物的光合作用,但过量后则会引起植物的光合速率下降;(2)当植物生长受氮限制时,在一定程度上的氮沉降增加植物生产力,但当氮过量后,氮沉降则使植物的生产力下降;(3)过量的氮沉降导致植物体各种营养元素含量的比例失衡;(4)氮沉降会改变植物的形态结构,集中表现为根/冠比减小;(5)氮沉降会增加植物对天然胁迫如干旱、病虫害和风的敏感性,减少其抵御能力;(6)氮沉降会改变植物组成和降低森林植物的多样性。

Human activities such as combustion of fossil fuels, intensive agriculture and stockbreeding, have significantly altered the global nitrogen cycle in the last several decades, increasing the concentrations of nitrogenous compounds in the atmosphere and rising the consequent N deposition to the global surface by several folds. As N is usually a limiting nutrient in most terrestrial ecosystems, additional N inputs to forest ecosystems may influence the growth, functioning and dynamics of those receiving forests. Based on available scientific evidence, we reviewed the impacts of N deposition on forest plants. The potential impacts were related to the following six aspects: (1) N deposition to some degree promotes photosynthetic rate, which is significantly correlated with leaf N concentration, as N deposition increases the leaf N concentration. However, when N deposition exceeds the nutritional demands of plants, it would reduce net photosynthesis by decreasing the concentrations of chlorophyll and Rubisco and activity of Rubisco in the leaves. (2) As N deposition increases the availability of N in soils, it would increase the productivity of plants at least in the short term. However, excess N inputs would lead to a reduction of productivity of plants. (3) Excess N deposition lead to an increasing leaching loss of cations as counterbalancing ions of leached nitrate, resulting in reduced amounts of exchangeable cations in forest soil. . Moreover, soil acidification promoted by N deposition increases the mobilization of toxic Al 3+ . These combined with disproportionately high N concentration in soil lead to nutritional imbalance in plants. (4) N deposition is likely to cause a morphological change of plants, especially on the shoot/root ratios, because N deposition tends to promote growth of aboveground plants and inhibit root growth. (5) The susceptibility of plants to secondary stress factors such as frost, drought and fungal pathogens or insect pests, is increased by high N loading. (6) N deposition changes species composition and decrease plant diversity in forest ecosystems.