不同水分条件下毛果苔草枯落物分解及营养动态

于2009年5月至2010年5月采用分解袋法,研究了三江平原典型湿地植物毛果苔草枯落物分解对水分条件变化的响应,探讨了典型碟形洼地不同水位下枯落物分解1a时间内的分解速率与N、P等营养元素动态。分解1a内,无积水环境下枯落物失重率为34.99%,季节性积水环境下为27.28%,常年积水环境下随水位增加枯落物失重率分别为26.99%与30.67%,表明积水条件抑制了枯落物的分解。枯落物的分解随环境变化表现出阶段性特征,分解0—122 d内随水位增加枯落物失重率分别为16.09%、24.25%、23.53%与26.60%,即生长季内积水条件促进了枯落物有机质的分解及重量损失。而随实验进行,分解122—360 d内随水位增加毛果苔草枯落物的失重率分别为18.90%、3.02%、3.46%、4.03%,即在非生长季土壤冻融期积水条件抑制了枯落物分解(P<0.05)。水分条件对毛果苔草枯落物N元素的影响表现为积水条件促进生长季内枯落物的N固定,水位最高处毛果苔草N浓度显著高于无积水环境(P<0.05)。但进入冻融期后积水环境下枯落物N浓度与含量降低;其中季节性积水限制了枯落物的N积累能力,至分解360d时与初始值相比表现出明显的N释放(P=0.01)。毛果苔草枯落物分解61d时P出现富集,其中积水条件下P的富集作用增强,但与水位不相关。分解1a后毛果苔草枯落物表现为P的净释放,不同水分条件下枯落物P元素损失没有明显差异(P>0.05)。

Litter decomposition and nutrient dynamics of Carex lasiocapa under different water conditions

A great research effort addressed the effect of plant litter decomposition on nutrient cycling in terrestrial and aquatic ecosystems.Environmental factors such as temperature and moisture content related to the decomposition process have been widely studied,and among the hydrological condition is more important and has quite complicated influence.In the present study,we investigated the effects of water conditions on decomposition and nutrient(N and P) dynamics of Carex lasiocapa litters using litter bag method in the Sanjiang Plain of Northeast China.The litter decomposition study was carried out in a typical dish-shaped pit along a water table gradient from May in 2009 to May in 2010.60 nylon bags(approx 1mm diameter) with 8g C.lasiocapa litters were placed near the soil surface or the grass layer in the marsh under unflooded or flooded conditions,with 12 under every water condition.3 bags in each site were taken back to the laboratory every time and then the mass losses and nutrient elements(N and P) contents were analyzed.By the end of decomposition,mass loss of C.lasiocapa litters was 34.99% and 27.28% under non-waterlogging and seasonally inundated conditions,respectively.In the permanently inundated conditions,with increased water table,litter mass loss ranged from 26.99% to 30.67%.The results showed that during the growing season(from May to September),C.lasiocapa litter decayed quickly in the flooded conditions.With increased water table gradient,the mass losses were 16.09%、24.25%、23.53% and 26.60% in non-waterlogging,seasonally inundated and permanently inundated condition,respectively.However,during the non-growing season,though higher water table accelerated the C.lasiocapa litter decomposition slightly in the inundated environment,flooded conditions significantly inhibited the litter decay compared to the dry condition(P<0.05).With increased water table gradient,the litter mass losses were 18.90%,3.02%,3.46% and 4.03% in non-waterlogging,seasonally inundated and permanently inundated conditions,respectively.In the growing season,litter N concentration and total N content increased gradually in the early 122 days of decomposition.Waterlogging conditions enhanced litter N immobilization,and litter N concentration under the deepest standing water condition was significantly higher than that under the dry condition(P<0.05).However,litter N concentration and total N content declined in the freeze-thawing season,and all the litters under flooded conditions released N after 122 days of decomposition.In addition,seasonal inundated conditions significantly inhibited litter N accumulation,and litter N content was significantly lower than the initial value after 360 days of decomposition(P=0.01).Moreover,litter P content significantly increased after 61 days of decomposition,especially in the flooding conditions.However,litter P enrichment had no correlation to water table depths.For all litter decomposition treatments,litter P concentration and total P content decreased after one year of decomposition,but did not vary with water table(P>0.05).Our results suggested that,in the Sanjiang Plain of Northeast China,the effect of water table on litter decomposition varied with decomposition stage,and flooding conditions stimulated litter decomposition in the growing season in the freshwater marshes.