荒漠河岸林优势种凋落物分解机制研究

Desert riparian forest is the main vegetation communities in extreme arid regions of Xinjiang. It has a vital role to improve the ecological environment,contain desertification, protect biodiversity and so on . In recent years, the upstream water supply has been dwindled, the River drying phenomena in the downstrem has often happened，because of the massive irrational land and water use along the Tarim River. Those lead to the fragile desert riparian forests severely damaged. Meanwhile, with the deterioration of the soil, water and salt environment, the coastal vegetation communities have shown the gradually decline trend. Litter as a nutrient carrier is the primary part of the forest ecosystem and the basis soil material which is critical role to improve tree nutrition and forest productivity, maintain the ecosystem balance. With the background of riparian vegetation degradation and poor management in the desert , this study will be established. And the research on typical desert riparian vegetation communities of litter decomposition mechanism will be carried out to recognize the desert riparian vegetation litter decomposition characteristics, understand effect between the biological and abiotic environment to the litter decomposition and interaction characteristics between environmental factors, seek the restrictive key factors to decomposition of various types of litter and illustrate the forest litter effect to the desert riparian forest ecosystem nutrient cycling. This study will provide the necessary theoretical basis and data support for sustainable management of the desert riparian forest vegetation.

荒漠河岸林是新疆极端干旱地区主要植被群落，对改善生态环境，遏制沙漠化，保护生物多样性等方面具有重大作用。近年来，由于塔里木河流域大规模不合理的水土开发利用，上游水源不断减少，下游断流现象不断发生，导致本来脆弱的荒漠河岸林严重受损。同时，伴随该地区土壤水分、盐分环境的恶化，沿岸植被群落已呈现出逐步衰退的迹象。凋落物作为养分的基本载体是生态系统的组成部分和森林土壤物质转化的基础, 对改善树木营养和提高森林生产力, 保持生态系统平衡, 有极为重要的作用。本研究是在荒漠河岸植被退化严重，经营管理不善的背景下立项，开展荒漠河岸典型植被群落凋落物分解机制研究，摸清荒漠河岸植被凋落物分解特性，了解生物环境和非生物环境对凋落物分解的影响及其各因子之间相互作用规律，寻求制约各类型凋落物分解的关键因子，明确森林凋落物对荒漠河岸森林生态系统养分循环的作用，为荒漠河岸森林可持续经营提供必要的理论基础和数据支撑。

以干旱区荒漠河岸优势种胡杨、多枝柽柳、胀果甘草为研究对象，采取凋落袋法，在干旱、盐生两种生境条件下进行凋落物分解试验。测定凋落物分解特征、林内微生境以及土壤生物化学特性动态变化，探讨不同生境下凋落物分解机理，明确各因子之间相互作用规律，寻求制约凋落物分解的关键因子。结果表明：①在干旱生境、盐生环境境条件下，经过360d分解，胡杨叶剩余率分别为79.03%、84.3%，胀果甘草剩余率为59.7%、81.13%，多枝柽柳分别为88.03%、86.64%。②在干旱、盐生生境条件下，胡杨凋落物分解常数分别是0.2353、0.1710，胀果甘草凋落物分解常数分别为0.5158、0.2126，多枝柽柳凋落物分解常数分别为0.1269、0.1520。胡杨凋落物分解t0.5分别为2.95a和4.12a, t0.95分别是12.75 a、17.80 a。胀果甘草凋落物分解t0.5分别为1.34a、3.62a, t0.95为5.81a、15.66a。多枝柽柳生境凋落物t0.5为5.56a和4.69a，t0.95为24.024a和20.28a。③经过360d分解，胡杨叶凋落物氮残留量分别为干旱生境56.3％＞盐生生境45.73％，磷元素残留量分别干旱生境为47.7％、盐生生境为40. 06％，有机碳的残留量分别为59.26％、87.8％；胀果甘草叶凋落物氮残留量分别为46.2%、48.45%，磷元素分别为干旱生境65.0％、盐生生境64.6％，有机碳的残留量分别为干旱生境为59.37％、盐生生境为72.25％；多枝柽柳在两个生境氮的绝对残留量分别为79.21%、75.01%，磷元素残留量盐生生境为62.4%、干旱生境为78.2％。有机碳的残留量从大到小的顺序为盐生生境80.85％、干旱生境78.71％。④土壤温湿度增加能够加快凋落物的分解，3种植物凋落物分解速率与土壤温度呈正比。在干旱生境中，土壤过氧化氢酶酶活性与凋落物分解量呈正相关，在盐生生境中则呈负相关。两个生境中，土壤蔗糖酶和碱性磷酸酶活性与凋落物的分解量呈正相关。