固氮和非固氮树种细根年生长动态及对供氮的响应

发布时间：2018-09-05 09:06

【摘要】：林木的细根(直径5 mm)是影响树木生长发育的重要器官。担负着吸收土壤中养分、水分的作用。森林生态系统中细根的生长变化一方面关乎该生态系统的C、N循环,另一方面对整个林分生产力水平的高低也有重要影响。近年来森林生态系统面临的新形势是土壤施肥量逐年增大与大气氮沉降,在此大背景影响下,细根生长动态的变化将对森林生态系统的碳氮循环发挥更重要影响。本文以生长在不同立地条件下的固氮树种(合欢和刺槐)与非固氮树种(马尾松、杉木)为研究对象,在施氮肥处理下,采用微根管技术对不同土层细根的年生长动态进行了观察与分析。以期明确细根动态对土壤N有效性的响应,为全球变化背景下的森林生态功能预测提供依据,为当前森林的集约生产与科学施肥提供科学支持。具体研究结果为:(1)固氮与非固氮两类树种的细根在不同立地条件下的年生长动态:在一个生长周期内,野外林分细根的总根长、总表面积、平均直径及总体积有明显的季节动态,即在7至9月份出现峰值,之后逐渐下降,12月份最低,次年1月份起开始逐渐缓慢回升;温室盆栽条件下,细根的各生长指标没有随季节表现明显变化,整体呈上升趋势。(2)不同生长条件下增施氮肥对细根生产的规律:施氮肥降低了野外林分固氮和非固氮树种的细根总根长、总表面积生产量,而温室盆栽苗木的细根生产增加。对野外样地而言,土壤中N的有效性与两类树种的细根年生产量之间存在负相关性,即土壤中N含量越高,则细根年生产量越低,在固氮与非固氮树种中呈现相同规律。此外,与非固氮树种相比,固氮树种的细根生产量在施肥样地与对照样地的差异较小。施氮肥增大温室盆栽条件下两类树种的细根生产,这可能与生长环境、林龄及生产方式的不同有关。(3)不同土层的固氮与非固氮树种细根年生长动态试验表明:不同土层在固氮与非固氮树种的对照样地和施肥样地细根年生长动态规律一致,都是在7到9月份出现峰值接着逐渐下降直到12月份降至最低点后,次年1月份再缓慢增加。此外随着土层深度的增加细根的各形态指标均有不同程度的增加。即本研究中20-40 cm土层相较于0-20 cm土层从总根长、总表面积、平均直径和总体积来看更有利于细根生长。(4)对不同环境条件下的细根年生长动态对比表明:在野外条件下合欢较其他三个树种的细根生长更多,其中合欢对照组在细根的各形态指标上数值最高;在温室盆栽条件下,各树种细根生长差异不明显。以上研究结果表明,在野外林分细根生长有明显的季节动态,并且增施氮肥降低了细根生长;而温室盆栽细根生产没有明显的季节波动,且施肥有利于细根生长。不同土层间细根生长动态一致,但较深土层细根数量更多,更有利于细根的生长。这些研究结果将对进一步了解固氮与非固氮树种细根动态在不同生态环境中的变化机制及明确细根的分布状况和森林地下的C循环提供必要的参考。
[Abstract]:Fine roots (5 mm in diameter) are important organs that affect the growth and development of trees. They absorb nutrients and water from the soil. The growth and change of fine roots in forest ecosystem is related to the C and N cycles of the ecosystem on the one hand, and the productivity level of the whole forest on the other. Under this background, the change of fine root growth dynamics will play a more important role in carbon and nitrogen cycling in forest ecosystems. In this paper, nitrogen-fixing and non-nitrogen-fixing tree species (Pinus massoniana, Chinese fir) growing under different site conditions were studied. The annual growth dynamics of fine roots in different soil layers were observed and analyzed by using microtubule technique under nitrogen fertilization, in order to clarify the response of fine roots dynamics to soil N availability, to provide basis for forest ecological function prediction under the background of global change, and to provide scientific support for intensive forest production and scientific fertilization. The results were as follows: (1) The annual growth dynamics of fine roots of nitrogen-fixing and non-nitrogen-fixing tree species in different site conditions: in one growth cycle, the total root length, total surface area, average diameter and total volume of fine roots in field stand had obvious seasonal dynamics, that is, peak value appeared from July to September, then gradually declined, the lowest in December, starting from January next year. The growth indices of fine roots did not change significantly with the season and showed an upward trend under potted greenhouse conditions. (2) The regularity of fine roots production under different growth conditions was that nitrogen fertilizer reduced the total root length and total surface area production of nitrogen-fixing and non-nitrogen-fixing trees in the field, while potted greenhouse planting decreased the total root length and total surface area production of fine roots. For field plots, the availability of N in soil was negatively correlated with the annual production of fine roots of two species, i.e. the higher the N content in soil, the lower the annual production of fine roots, and the same pattern was observed in nitrogen-fixing and non-nitrogen-fixing species. There was little difference between the fertilized plots and the control plots. Nitrogen fertilization increased the fine root production of the two tree species under pot culture in greenhouse, which might be related to the growth environment, forest age and production mode. (3) The annual growth dynamics of fine roots of nitrogen-fixing and non-nitrogen-fixing tree species in different soil layers showed that the control plots of nitrogen-fixing and non-nitrogen-fixing tree species in different soil layers were different. The annual growth dynamics of fine roots in soil and fertilizer plots were the same. They all increased slowly in January of the following year after peaking from July to September and then decreasing gradually until the lowest point in December. (4) The annual growth dynamics of fine roots under different environmental conditions showed that the growth of fine roots of Albizzia julibrissin was more than that of other three tree species in the field, and the value of fine roots morphological indexes in the control group was the highest. The results showed that the growth of fine roots had obvious seasonal dynamics in field stands, and the growth of fine roots was decreased by increasing nitrogen fertilizer. The production of fine roots in greenhouse had no obvious seasonal fluctuation, and fertilization was conducive to the growth of fine roots. These results will provide a necessary reference for further understanding the mechanism of fine root dynamics of nitrogen-fixing and non-nitrogen-fixing tree species in different ecological environments and for clarifying the distribution of fine roots and the C cycle underground.
【学位授予单位】：华中农业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S718.43

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