大气CO_(2)浓度升高和海平面上升对滨海湿地植物地下生物量的影响

大气CO_(2)浓度升高和海平面上升会通过影响植物的分布和生长状况,继而影响湿地的稳定性。地下生物量是调节潮汐湿地生态系统功能的关键因素,包括土壤有机质的积累和湿地海拔高程的维持。本文通过设置开顶式生长箱(OTC:open top chamber)试验探究不同海拔的3个典型植物群落(SC群落:C_(3)植物为主的群落;MX群落:C_(3)、C_(4)植物混合群落;SP群落:C_(4)植物为主的群落)对CO_(2)浓度升高和海平面上升的响应差异。研究结果显示:CO_(2)浓度升高能够显著增加SC、MX和SP群落的根茎、根和总地下生物量,但年际差异较大。海平面上升显著降低了3个群落植物的根生物量和SC群落高CO_(2)浓度处理下及SP群落对照处理下的总地下生物量,但对根茎却无显著影响。在高盐的条件下,高CO_(2)浓度一定程度上能够缓解高盐分对植物的胁迫,但高CO_(2)浓度的施肥作用下降。对照条件下的SC和MX群落总地下生物量随试验年份延长呈下降趋势,其下降主要是由于海平面的快速上升导致的,而高CO_(2)浓度能减缓其下降趋势,一定程度上抵消胁迫。因此,海平面上升正严重威胁未来湿地的稳定性,而CO_(2)浓度升高能一定程度上缓解海平面上升的危害。

Effects of Grazing Exclusion on Plant Productivity and Soil Carbon, Nitrogen Storage in Alpine Meadows in Northern Tibet, China

Grazing exclusion is widely adopted in restoring degraded alpine grasslands on the Qinghai-Tibetan Plateau. However, its effectiveness remains poorly understood. In this study, we investigated the effects of grazing exclusion on plant productivity, species diversity and soil organic carbon(SOC) and soil total nitrogen(STN) storage along a transect spanning from east to west of alpine meadows in northern Tibet, China. After six years of grazing exclusion, plant cover, aboveground biomass(AGB), belowground biomass(BGB), SOC and STN were increased, but species diversity indices declined. The enhancement of AGB and SOC caused by grazing exclusion was correlated positively with mean annual precipitation(MAP). Grazing exclusion led to remarkable biomass increase of sedge species, especially Kobresia pygmaea, whereas decrease of biomass in forbs and no obvious change in grass, leguminous and noxious species. Root biomass was concentrated in the near surface layer(10 cm) after grazing exclusion. The effects of grazing exclusion on SOC storage were confined to shallow soil layer in sites with lower MAP. It is indicated that grazing exclusion is an effective measure to increase forage production and enhance soil carbon sequestration in the studied region. The effect is more efficient in sites with higher precipitation. However, the results revealed a tradeoff between vegetation restoration and ecological biodiversity. Therefore, carbon pools recover more quickly than plant biodiversity in the alpine meadows. We suggest that grazing exclusion should be combined with other measures to reconcile grassland restoration and biodiversity conservation.

氮素与水分添加对内蒙古温带典型草原生物量的影响

为了解大气氮沉降和降水格局改变对草原生物量的影响,在内蒙古温带典型草原开展氮、水添加控制试验.试验设置对照(CK),氮素添加(10 g m^(-2) a^(-1)),水分添加(60 mm m^(-2) a^(-1)),氮、水同时添加(N 10 g m^(-2) a^(-1)+水60 mm m^(-2) a^(-1))4种处理.经过两年试验处理,结果显示:(1)较对照处理,氮添加处理下总生物量(403.03 g/m^2)、地上生物量(279.97 g/m^2)、地下生物量(123.07 g/m^2)和禾类草地上生物量(165.35 g/m^2)均显著增加,而杂类草地上生物量变化不显著.(2)水添加较对照显著增加了地上生物量(200.93 g/m^2)、杂类草地上生物量(177.82 g/m^2),但显著降低了地下生物量(-110.39 g/m^2),而总生物量与禾类草地上生物量变化不显著.(3)氮添加处理下,水添加显著增加了地下生物量与禾类草地上生物量,但对总生物量、地上生物量、杂类草地上生物量没有显著影响.进一步分析显示,在不添加水分条件下,氮添加较对照显著增加禾类草地上生物量(107.15 g/m^2)与地下生物量(5.43 g/m^2);而在水分添加条件下,氮添加较对照分别增加58.2 g/m^2和117.64 g/m^2.本研究结果表明,禾类草地上生物量与其氮含量呈正相关关系,杂类草地上生物量与土壤含水量呈正相关关系,这可能是氮素添加提高禾类草地上生物量和水分添加提高杂类草地上生物量的重要机制之一;在内蒙古干旱半干旱地区仅氮素添加(10 g m^(-2) a^(-1))的措施可显著增加禾类草的地上生物量,有利饲草产量的增加,如需增加菊科、豆科等其他杂草的生物量,可考虑水分的补给.