| 摘要 | 土壤呼吸不仅是导致全球气候变化的关键性生态学过程，而且在陆地
生态系统碳循环过程中具有极其重要的作用。黄土高原沟壑区地形复杂，
土地覆盖多样。研究不同土地利用条件下土壤呼吸变化规律是准确估计黄
土区碳循环的基础。以中国科学院长武黄土高原农业生态试验站为研究基
地，针对退耕人工林地、退耕草地，利用Li-8100 系统(Li-COR, Lincoln, NE,
USA)监测土壤呼吸动态变化、并同时测定了土壤温度、土壤水分变化，研
究了退耕还林还草条件下，黄土高原沟壑区农地、草地、林地土壤呼吸变
化及其与土壤水分、温度的关系，重点回答以下科学问题：
刺槐人工林地表凋落物对土壤呼吸的贡献？
退耕还草是否导致土壤呼吸的改变？
退耕还林还草条件下非生物因素（水分、温度）的变化是否影响土壤
呼吸？
主要获得以下结果：
地表凋落物积累影响土壤呼吸及其陆地生态系统碳蓄积
添加或去除凋落物显著影响土壤呼吸（p = 0.091–0.099），与对照（CK）
的土壤呼吸速率（3.23 μmol m-2 s-1）相比，添加凋落物（DL）使土壤呼吸
速率增加26%，去除凋落物使土壤呼吸速率减少22%。NL、CK 和DL 的累
积土壤呼吸分别为631、787 和973 g C m-2 year-1。地表凋落物对土壤呼吸
年平均贡献量为20%。刺槐人工林地表凋落物的输入量为213 g C m-2 year-1，
大于凋落物引起的呼吸量156 g C m-2 year-1。因此，在黄土区通过植被恢复
治理水土流失过程中，随着地表凋落物的积累，林地生态系统的碳汇功能
将逐步得到加强。相似条件下土地利用方式变化影响土壤呼吸
土壤呼吸速率因土地利用方式的改变而发生了显著的变化。整个试验
期间，草地土壤呼吸速率较农田提高了24%（p < 0.05）。农田土壤呼吸速率
平均值1.35μmol·（m2·s）-1；草地土壤呼吸速率平均值1.67μmol·（m2·s）-1。
2011 年，农田和草地累积土壤呼吸分别为413 g·m-2 和517 g·m-2，草地比农
田提高了25%。本研究表明，两个生态系统中，土壤水分（0~5 cm）与土
壤呼吸无显著相关关系；土壤温度是土壤呼吸变化的重要驱动因素。协方
差分析（ANCOVA）表明，草地和农田生态系统中土壤呼吸对土壤温度的
响应存在本质差异。
环境变化（水分、温度）对土壤呼吸的影响
在林地生态系统中，试验期间各处理平均土壤温度高低趋势为DL > NL
> CK，但差异不显著（p = 0.48）。与土壤温度变化相似，试验期间各处理
土壤水分随时间逐渐升高，各处理土壤水分平均值差异显著（p < 0.01）。
DL，NL 和CK 处理土壤呼吸速率与土壤温度呈显著的指数关系（R2 =
0.81–0.90，p < 0.0001），但与土壤水分的关系不明显。NL、CK 和DL 的
Q10 依次为1.92、2.29 和2.31。相关性分析表明，各测定日地表凋落物贡献
与土壤温度（r = 0.54，p < 0.05）或土壤水分关系显著（r = 0.68, p < 0.05）。
在农田和草地生态系统中，试验期间，农田与草地的土壤温度差异显
著，草地平均土壤温度（14.9℃）较农田（12.4）高2.5℃（p < 0.05）。农田
平均土壤水分含量农田15.5 %，草地14.4%,二者的差异并不显著。农田和
草地生态系统土壤温度与土壤呼吸均呈显著的指数关系（p < 0.0001）。但农
田和草地生态系统中土壤呼吸对温度响应存在本质差异（α = 0.05），农田土
壤呼吸的温度敏感性（Q10）（2.13）高于草地（1.81）。农田与草地的土壤温
度差异能够解释两种土地利用方式导致的土壤呼吸差异,但土壤水分与土
壤呼吸无显著相关关系，土地利用方式间土壤水分变化不能解释农田与草
地条件下土壤呼吸的显著差异。
关键词: 刺槐人工林；土壤呼吸；黄土高原; 农田; 草地 |
| 其他摘要 | Soil respiration is the key ecological process, and plays an important role in
carbon cycle of terrestrial ecosystem. Gullied Loess Plateau was with
fragmented topographies, diverse land use cover. Understanding soil respiration
under different landuses conditions is critical to estimate carbon cycle at regional
scale in Loess Plateau of China. At the present study, soil CO2 emission in
cropland, grassland and woodland ecosystem was measured by an automated
soil CO2 system (Li-8100, Li-COR, Lincoln, NE, USA) in the Loess Plateau.
The relations of soil CO2 emission to soil moisture, and soil temperature were
explored among the three ecosystems of cropland, grassland and woodland. Our
objectives at the present study are as follows:
First, study the contribution of aboveground litter in the black Locust
Plantation.
Second, in cropland and its adjacent grassland, we determined if landuse
change could alter soil CO2 efflux under similar edaphic and climate conditions
with conversion of arable land into grassland or forest land.
Third, what are the effects of water and temperature on soil respiration
when arable land is converted into grassland or forest land.
The main results of this study are as follows:
Aboveground litter accumulation can affect soil respiration and the carbon
accumulation of the terrestrial ecosystems. DL significantly increased Rs in CK
by 26% (p = 0.091) while NL significantly decreased Rs in CK by 22% (p =
0.099). The cumulative CO2-C emissions from NL, CK and DL were 631, 787
and 973 g C m-2 year-1, respectively. And annual mean contribution rate of
aboveground litter to soil respiration was 20%. The aboveground litterfall was 213 g C m-2 year-1, which was greater than the release of C from the respiration
caused by aboveground litter (156 g C m-2 year-1). This result has strong
implications for soil C storage, indicating that aboveground litter accumulation
in this young black locust plantation may be expected to continue contribute the
carbon pool in the ecosystem undergoing vegetation restoration and soil
conservation measures on the Loess Plateau, at least in the near future.
In cropland and its adjacent grassland, landuse change could alter soil CO2
efflux under similar edaphic and climate conditions. We found marked
differences in soil respiration related to different landuse: the mean cropland soil
respiration (1.35 μmol m-2s-1) averaged 24% less than paired grassland soil
respiration (1.67 μmol m-2s-1) (p < 0.05) during the period of experiment. The
extent of soil respiration of cropland varied from -0.02 to 3.41μmol m-2s-1 and its
mean value was 1.67μmol m-2s-1. The grassland was varied from 0.12 to 3.83 μmol
m-2s-1, and its mean value was 1.67 μmol m-2s-1. The difference was occurred in
summer and autumn, which was higher. In summer and autumn, the mean values
of soil respiration of cropland was 2.19 and 1.18 μmol m-2s-1, which grassland
was 25% and 32% higher than the values of cropland. And the cumulative
CO2-C emission in grassland (856 g C m-2) was 23% higher than that in cropland
(694 g C m-2).
The effects soil water or temperature on soil respiration under the
conditions of environmental change. In woodland ecosystem, the temperature of
different treatments showed an order of DL > NL > CK, but there was no
significant difference among them. Like soil temperature, soil moisture
increased with time going on. The moisture had a significant difference among
these treatments （ p < 0.01 ） . The Rs of NL, CK and DL had significant
exponential correlation (R2 = 0.81 to 0.90; p < 0.0001) with soil temperature but
had unclear relationships with soil moisture. The temperature sensitivity of soil
respiration, Q10, in NL, CK and DL was 1.92, 2.29 and 2.31, respectively.
Correlation analysis showed that litter contribution on every measurement day
had significant positive correlativity with soil temperature (r = 0.54, p < 0.05) or
moisture（r = 0.68, p < 0.05）.
In cropland and grassland ecosystem, soil temperature at 5cm was 2.5 ℃
higher in grassland during the period of experiment (p < 0.05). The moisture of cropland was 15.5%, grassland 14.4%, that is, there was no significant between
them. Regression of soil temperature vs. soil respiration indicated significant
exponential relationships both in grassland and cropland, explaining 79% of the
variation in soil respiration in grassland, compared to 82% in cropland. Besides,
there were intrinsic differences in response of soil respiration to temperature
between the cropland and grassland ecosystems: grassland and cropland
respiration response was significantly different at the α = 0.05 level, also
expressed by a higher temperature sensitivity of soil respiration (Q10) in cropland
(2.13) relative to grassland (1.81). Soil temperature difference between cropland
and grassland can explain the Rs difference caused by landuse change, which
was confirmed by the validation results. But soil moister that have unclear
relationship with soil respiration cannot explain.
Keywords: Black Locust Plantation; Soil Respiration; Loess Plateau; Cropland;
Grassland |
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