基于高分和哨兵卫星影像研究氮沉降对杨树人工林的影响

Assessing the impacts of nitrogen deposition on poplar plantation based on Gaofen and Sentinel imagery

氮沉降会对生态系统产生多方面的影响,而现有的森林生态系统对氮沉降的响应研究主要集中在短期的即时性影响上,因此迫切需要关注氮沉降对森林生态系统的长期影响。为了解不同氮沉降水平对杨树人工林在长时间序列上的影响,从2012年开始,在起始林龄为8年的杨树(Populus deltoides)人工林开展连续7年的模拟氮沉降试验,氮添加水平分别为空白对照(0 kg·hm^(-2)·a^(-1))、低氮处理(N1,50 kg·hm^(-2)·a^(-1))、中氮处理(N2,100kg·hm^(-2)·a^(-1))、高氮处理(N3,150 kg·hm^(-2)·a^(-1))和超高氮处理(N4,300 kg·hm^(-2)·a^(-1)),通过高分(GF1、GF2)和哨兵(Sentinel-2)高空间分辨率卫星遥感手段提取杨树NDVI值并分析其动态变化,研究不同氮沉降水平在长时间序列上对杨树人工林生长的影响。结果表明:经过2年的模拟氮沉降,4个氮添加样地杨树NDVI值分别增加2.0%、4.8%、4.3%和4.5%,均达到了最大增长率;经过4年的模拟氮沉降,各氮添加处理的杨树NDVI值均大于对照,表现为对杨树生长具有促进作用,但这种促进作用在第3年后是整体减弱的;经过6年的模拟氮沉降,中低氮处理仍然对杨树表现为促进作用,而高氮和超高氮处理则对杨树表现为抑制作用,且随着氮添加水平的增高,这种促进作用逐渐减弱而抑制作用逐渐增强。

Nitrogen deposition has multiple effects on forest ecosystems.Previous related studies mainly focused on immediate effects in the short term.It is critically needed to study long-term impacts of nitrogen deposition on forest ecosystems.To understand the effects of nitrogen deposition with different levels on forest ecosystem,a simulated nitrogen deposition experiment was conducted in a 8-year-old poplar(Populus deltoides)plantation since 2012,with the treatments of CK(0 kg·hm^(-2)·a^(-1)),low nitrogen deposition(N1,50 kg·hm^(-2)·a^(-1)),medium nitrogen deposition(N2,100 kg·hm^(-2)·a^(-1)),high nitrogen deposition(N3,150 kg·hm^(-2)·a^(-1)),and ultrahigh nitrogen deposition(N4,300 kg·hm^(-2)·a^(-1)).The effects of nitrogen addition on the growth of poplar plantation over long time series was examined using Gaofen(GF1,GF2)and Sentinel(Sentinel-2)satellite images by extracting poplar NDVI values.The results showed that the NDVI values of poplar trees were increased by 2.0%,4.8%,4.3%,and 4.5%in the four N treatments,respectively.The maximum growth rate occurred after treated for two years.After four years of treatment,the NDVI values of poplar trees under nitrogen addition were all greater than that of the CK,which indicated that nitrogen deposition had positive effects on poplar growth.However,such promotion effects were overall weakened after three years.After being treated for six years,medium and low nitrogen deposition had a promoting effect on poplar growth,but high and ultrahigh nitrogen treatment had an inhibiting effect.Overall,the promoting effect was gradually weakened while the inhibiting effect was gradually enhanced with increasing nitrogen addition levels.