【摘要】：林木的細(xì)根(直徑5 mm)是影響樹木生長(zhǎng)發(fā)育的重要器官。擔(dān)負(fù)著吸收土壤中養(yǎng)分、水分的作用。森林生態(tài)系統(tǒng)中細(xì)根的生長(zhǎng)變化一方面關(guān)乎該生態(tài)系統(tǒng)的C、N循環(huán),另一方面對(duì)整個(gè)林分生產(chǎn)力水平的高低也有重要影響。近年來森林生態(tài)系統(tǒng)面臨的新形勢(shì)是土壤施肥量逐年增大與大氣氮沉降,在此大背景影響下,細(xì)根生長(zhǎng)動(dòng)態(tài)的變化將對(duì)森林生態(tài)系統(tǒng)的碳氮循環(huán)發(fā)揮更重要影響。本文以生長(zhǎng)在不同立地條件下的固氮樹種(合歡和刺槐)與非固氮樹種(馬尾松、杉木)為研究對(duì)象,在施氮肥處理下,采用微根管技術(shù)對(duì)不同土層細(xì)根的年生長(zhǎng)動(dòng)態(tài)進(jìn)行了觀察與分析。以期明確細(xì)根動(dòng)態(tài)對(duì)土壤N有效性的響應(yīng),為全球變化背景下的森林生態(tài)功能預(yù)測(cè)提供依據(jù),為當(dāng)前森林的集約生產(chǎn)與科學(xué)施肥提供科學(xué)支持。具體研究結(jié)果為:(1)固氮與非固氮兩類樹種的細(xì)根在不同立地條件下的年生長(zhǎng)動(dòng)態(tài):在一個(gè)生長(zhǎng)周期內(nèi),野外林分細(xì)根的總根長(zhǎng)、總表面積、平均直徑及總體積有明顯的季節(jié)動(dòng)態(tài),即在7至9月份出現(xiàn)峰值,之后逐漸下降,12月份最低,次年1月份起開始逐漸緩慢回升;溫室盆栽條件下,細(xì)根的各生長(zhǎng)指標(biāo)沒有隨季節(jié)表現(xiàn)明顯變化,整體呈上升趨勢(shì)。(2)不同生長(zhǎng)條件下增施氮肥對(duì)細(xì)根生產(chǎn)的規(guī)律:施氮肥降低了野外林分固氮和非固氮樹種的細(xì)根總根長(zhǎng)、總表面積生產(chǎn)量,而溫室盆栽苗木的細(xì)根生產(chǎn)增加。對(duì)野外樣地而言,土壤中N的有效性與兩類樹種的細(xì)根年生產(chǎn)量之間存在負(fù)相關(guān)性,即土壤中N含量越高,則細(xì)根年生產(chǎn)量越低,在固氮與非固氮樹種中呈現(xiàn)相同規(guī)律。此外,與非固氮樹種相比,固氮樹種的細(xì)根生產(chǎn)量在施肥樣地與對(duì)照樣地的差異較小。施氮肥增大溫室盆栽條件下兩類樹種的細(xì)根生產(chǎn),這可能與生長(zhǎng)環(huán)境、林齡及生產(chǎn)方式的不同有關(guān)。(3)不同土層的固氮與非固氮樹種細(xì)根年生長(zhǎng)動(dòng)態(tài)試驗(yàn)表明:不同土層在固氮與非固氮樹種的對(duì)照樣地和施肥樣地細(xì)根年生長(zhǎng)動(dòng)態(tài)規(guī)律一致,都是在7到9月份出現(xiàn)峰值接著逐漸下降直到12月份降至最低點(diǎn)后,次年1月份再緩慢增加。此外隨著土層深度的增加細(xì)根的各形態(tài)指標(biāo)均有不同程度的增加。即本研究中20-40 cm土層相較于0-20 cm土層從總根長(zhǎng)、總表面積、平均直徑和總體積來看更有利于細(xì)根生長(zhǎng)。(4)對(duì)不同環(huán)境條件下的細(xì)根年生長(zhǎng)動(dòng)態(tài)對(duì)比表明:在野外條件下合歡較其他三個(gè)樹種的細(xì)根生長(zhǎng)更多,其中合歡對(duì)照組在細(xì)根的各形態(tài)指標(biāo)上數(shù)值最高;在溫室盆栽條件下,各樹種細(xì)根生長(zhǎng)差異不明顯。以上研究結(jié)果表明,在野外林分細(xì)根生長(zhǎng)有明顯的季節(jié)動(dòng)態(tài),并且增施氮肥降低了細(xì)根生長(zhǎng);而溫室盆栽細(xì)根生產(chǎn)沒有明顯的季節(jié)波動(dòng),且施肥有利于細(xì)根生長(zhǎng)。不同土層間細(xì)根生長(zhǎng)動(dòng)態(tài)一致,但較深土層細(xì)根數(shù)量更多,更有利于細(xì)根的生長(zhǎng)。這些研究結(jié)果將對(duì)進(jìn)一步了解固氮與非固氮樹種細(xì)根動(dòng)態(tài)在不同生態(tài)環(huán)境中的變化機(jī)制及明確細(xì)根的分布狀況和森林地下的C循環(huán)提供必要的參考。
[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.
【學(xué)位授予單位】：華中農(nóng)業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：S718.43

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