长期氮沉降对杉木人工林叶、枝氮磷养分再吸收的影响

为了解森林养分内循环对全球变化的响应, 基于长期模拟氮沉降试验, 研究了杉木(Cunninghamia lanceolata)人工林不同龄级(一年生、二年生和衰老)叶和枝的氮(N)、磷(P)养分分配及其再吸收特征, 并分析了不同模拟N沉降处理时间(7年和14年)杉木叶N、P养分再吸收差异。在12年生杉木中开展模拟N沉降试验, 以尿素(CO(NH₂)₂)为N源, 设N0、N1、N2和N3 4个处理水平, 施氮量分别为0、60、120和240 kg·hm ^-2·a ^-1, 每个处理重复3次。结果表明: (1)叶和枝在衰老过程中碳(C)、N和P含量逐渐降低, 且叶的C、N和P含量比枝高; N含量大小依次为一年生叶>二年生叶>衰老叶>一年生枝>二年生枝>衰老枝, 且N3 > N2 > N1 > N0, 而C:N则呈现相反的趋势; 衰老器官的C:N、C:P、N:P比新鲜器官高; N沉降增加了不同龄级叶和枝(除二年生叶外)的N、N:P和C:P, 但降低了P和C:N。(2)叶和枝的N、P养分再吸收率(RE_N、RE_P)随龄级的增加至衰老有规律地递减, 且RE_P > RE_N; 受长期N沉降的影响, RE_N叶(28.12%) <枝(30.00%), 而RE_P则为叶(45.82%) >枝(30.42%); 杉木叶和枝N:P与RE_N:RE_P之间存在极显著的线性相关关系。(3)随N沉降处理时间的增加, 叶RE_N呈降低态势, 各处理(N1、N2和N3)分别降低了9.85%、3.17%和11.71%; 而RE_P则明显上升, 分别增加了71.98%、42.25%和9.60%。研究结果表明: 不同器官、不同龄级的养分再吸收率随氮沉降处理的水平、处理时间而所有不同; RE_N:RE_P与N:P之间存在紧密关系。     

Short-term nitrogen fertilization decreased root and microbial respiration in a young Cunninghamia lanceolata plantation

Aims As the primary pathway for CO₂ emission from terrestrial ecosystems to the atmosphere, soil respiration is estimated to be 80 Pg C·a^-1 to 100 Pg C·a^-1, equivalent to 10 fold of fossil fuel emissions. As an important management practice in plantation forests, fertilization does not only increase primary production but also affects soil respiration. To investigate how nitrogen (N) fertilization affects total soil, root and microbial respiration, a N fertilization experiment was conducted in a five-year-old Cunninghamia lanceolata plantation in Huitong, Hunan Province, located in the subtropical region. MethodsOne year after fertilization, soil respiration was monitored monthly by LI-8100 from July 2013 to June 2014. Soil temperature and water content (0-5 cm soil depth) were also measured simultaneously. Available soil nutrients, fine root biomass and microbial communities were analyzed in June 2013. Important findings Total soil, root and microbial respiration rates were 22.7%, 19.6%, and 23.5% lower in the fertilized plots than in the unfertilized plots, respectively. The temperature sensitivity (Q₁₀) of soil respiration ranged from 1.81 to 2.04, and the Q₁₀ value of microbial respiration decreased from 2.04 in the unfertilized plots to 1.84 in the fertilized plots. However, neither the Q₁₀ value nor the patterns of total soil respiration were affected by N fertilization. In the two-factor model, soil temperature and moisture accounted for 69.9%-79.7% of the seasonal variations in soil respiration. These results suggest that N fertilization reduces the response of soil organic carbon decomposition to temperature change and may contribute to the increase of soil carbon storage under global warming in subtropical plantations.     

Effects of understory removal on soil respiration and microbial community composition structure in a Chinese fir plantation

Aims Soil respiration (R_s) is the largest fraction of carbon flux in forest ecosystems, but the effects of forest understory removal on R_s in Chinese fir (Cunninghamia lanceolate) plantations is poorly understood. In order to quantify the effects of forest understory removal on R_s and microbial community composition, a field experiment was conducted in a subtropical Chinese fir plantation. Methods Forest understory was removed manually in June 2012. R_s was measured monthly using a LI-COR 8100 infrared gas analyzer from July 2012 through July 2014. Soil temperature and moisture were also measured at 5 cm depth at the time of R_s measurements. Surface soil (0-10 cm) samples were collected in July 2013 and 2014, respectively, and the soil microbial community structures were determined by phospholipid fatty acids (PLFAs) analysis. Important findings R_s decreased by 32.8% over a two-year period following understory removal (UR), with a greater rate of decrease in the first year (42.9%) than in the second year (22.2%). The temperature sensitivity of R_s was affected by UR, and was 2.10 and 1.87 in the control and UR plots, respectively. UR significantly reduced the concentration of fungal PLFAs by 18.3%, but did not affect the concentration of bacterial PLFAs, resulting in an increase in the fungal:bacterial ratio; it significantly increased the concentration of gram-positive bacterial PLFAs by 24.5%, and the ratio of gram-positive to gram-negative bacterial PLFAs after one year of treatment, but decreased the concentration of gram-positive bacterial PLFAs by 9.4% and the ratio of gram-positive to gram-negative bacterial PLFAs after two years of treatment. The results suggested that R_s and microbial community composition were both affected by UR in Chinese fir plantation, and the effects were dependent of the duration following the UR treatment.     

Changes in nutrient cycling with age in a Cunninghamia lanceolata plantation forest

Aims The purpose of this study is to investigate the characteristics of nutrient cycling in Cunninghamia lanceolata plantations) with different ages, and to provide scientific basis for the management of high-yield plantations in China.     

Interactive effects of soil warming and nitrogen addition on fine root production of Chinese fir seedlings

Aims There have been a large number of studies on the independent separate responses of fine roots to warming and nitrogen deposition, but with contradictory reporting. Fine root production plays a critical role in ecosystem carbon, nutrient and water cycling, yet how it responds to the interactive warming and nitrogen addition is not well understood. In the present study, we aimed to examine the interactive effects of soil warming and nitrogen addition on fine root growth of 1-year-old Chinese fir (Cunninghamia lanceolata) seedlings in subtropical China.
Methods A mesocosm experiment, with a factorial design of soil warming (ambient, +5 °C) and nitrogen addition (ambient, ambient + 40 kg·hm^-2·a^-1, ambient + 80 kg·hm^-2·a^-1), was carried out in the Chenda State-owned Forest Farm in Sanming City, Fujian Province, China. Fine root production (indexed by the number of fine roots emerged per tube of one year) was measured biweekly using minirhizotrons from March of 2014 to February of 2015.
Important findings (1) The two-way ANOVA showed that soil warming had a significant effect on fine root production, while nitrogen addition and soil warming × nitrogen addition had no effect. (2) The three-way ANOVA (soil warming, nitrogen addition and diameter class) showed that soil warming, diameter class and soil warming × diameter class had significant effects on fine root production, especially for the number of fine roots in 0-1 mm diameter class that had been significantly increased by soil warming. Compared with the 1-2 mm roots, the 0-1 mm roots seemed more flexible. (3) Repeated measures of ANOVA (soil warming, nitrogen addition and season) showed that soil warming, season, soil warming × season, and soil warming × nitrogen addition × season had significant effects on fine root production. In spring, the number of fine roots was significantly increased both by soil warming and soil warming × season, while soil warming, nitrogen addition, soil warming × nitrogen addition significantly decreased fine root production in the summer. (4) Soil warming, soil layer, soil warming × soil layer had significant effects on fine root production. The number of in-growth fine roots was significantly increased by soil warming at the 20-30 cm depth only. It seemed that warming forced fine roots to grow deeper in the soil. In conclusion, soil warming significantly increased fine root production, but they had different responses and were dependent of different diameter classes, seasons and soil layers. Nitrogen addition had no effect on fine root production. Only in spring and summer, soil warming and nitrogen addition had significant interactive effects.     

杉木人工林凋落物生态化学计量与土壤有效养分对长期模拟氮沉降的响应

凋落物分解的快慢和养分释放的速度决定了生态系统中土壤有效养分的供应。探讨全球变化条件下森林生态系统凋落物与土壤养分的变化规律,有利于深入认识凋落物-土壤相互作用的养分调控因素,从而揭示生态系统C、N、P循环。通过模拟氮沉降增加试验,分4个水平处理,分别为0、60、120、240 kg N hm~(-2)a~(-1)。模拟氮沉降13年后,分析了杉木人工林凋落物中不同组分(落叶、落枝、落果)生态化学计量与土壤有效养分(有效氮、碱解氮、速效磷、速效钾)的关系。结果表明:氮沉降(N1、N2和N3)显著提高了落叶和落枝的N含量,平均增幅分别为35.27%和32.21%;高水平氮沉降(N3)处理显著降低了落叶和落枝的C/N,平均降幅分别为25.95%和22.32%,但N3增加了落枝和落果N/P,平均增幅分别为38.4%和31.7%;氮沉降对凋落物各组分的C、P和C/P均影响不显著。氮沉降处理显著增加了土壤NO_3~--N和NH_4~+-N含量,均表现为N3N2N1N0,其中NO_3~--N含量更容易受氮沉降处理的影响,表现为更大的增幅。N2显著增加0—20 cm土层的碱解氮含量,N1显著降低0—20 cm土层的速效钾,但氮沉降对速效磷含量没有影响。凋落物生态化学计量与土壤有效养分之间的Pearson相关和冗余分析(RDA)表明,凋落物生态化学计量与土壤有效养分之间关系紧密,凋落物P含量(蒙特卡罗检验,P=0.018)和C/P比值(P=0.037)对土壤有效养分影响显著。凋落物中C/N比值、C/P比值与土壤有效养分呈显著负相关,其比值越高越不利于土壤有效养分的累积。     

长期氮沉降下杉木人工林凋落物与土壤的C、N、P化学计量特征

为研究长期氮沉降条件下林木凋落物与土壤养分之间的关系,该文以亚热带杉木(Cunninghamia lanceolata)人工林为研究对象,分析了模拟氮沉降处理第12年时杉木林凋落物不同组分(叶、枝、果)与不同土层土壤(0～20 cm、20～40 cm、40～60 cm)的C、N、P含量及其化学计量比。氮沉降处理分4个水平,分别为N0(0 kg N·hm^-2·a^-1)、N1(60 kg N·hm^-2·a^-1)、N2(120 kg N·hm^-2·a^-1)、N3(240 kg N·hm^-2·a^-1),每处理重复3次。结果表明:(1)凋落物各组分的C、N、P含量及其化学计量比均高于土壤;凋落物和土壤化学计量比均表现为C/P>C/N>N/P;凋落物不同组分的C、N含量表现为叶>果>枝,而P含量表现为叶>枝>果。(2) 12 a氮沉降增加了凋落物叶、枝和果的N含量,增幅分别为4.24%、1...     

氮沉降下杉木(Cunninghamia lanceolata)人工林凋落叶分解过程中C、N元素动态变化

在12年生的杉木(Cunninghamia lanceolata)人工林中开展模拟氮沉降试验,分N0(对照)、N1、N2、N3等4种处理,N沉降量依次为0、60、120、240 kg N hm-2 a-1,每处理重复3次.通过2 a的监测和分析发现,经N0、N1、N2、N3处理后,凋落物分解过程中C平均含量分别为46.47%、46.35%、46.79%、46.6%,各处理之间无显著差异,但均随着分解时间的增加呈下降趋势.氮沉降明显增加了凋落物中的N含量,且随着沉降水平的增加而增加.各处理凋落物C的分解系数依次为0.739、0.744、0.936、0.708,周转期为4.26 a、4.26 a、3.46 a、4.41 a;而N的分解系数分别为0.458、0.543、0.776、0.565,周转期为6.26 a、5.44 a、3.91 a、5.20 a.N1处理表现出促进N释放的作用,但对C释放影响不明显;N2处理促进了凋落物C、N元素的释放,而N3处理则表现出一定的抑制作用.氮沉降处理也明显降低了凋落物的C/N比,N1、N2、N3处理使C/N比分别比N0下降8.59%、14.20%和17.54%.     

杉木人工林凋落物量对氮沉降增加的初期响应

通过野外模拟试验,研究了杉木人工林凋落物对氮沉降增加的初期响应。试验设计为4种处理,分别为N0(0kgN.hm-2.a-1,对照)、N1(60kgN.hm-2.a-1)、N2(120kgN.hm-2.a-1)、N3(240kgN.hm-2.a-1),3次重复。通过2年监测发现,对照样地的年凋落量为2427.51kg.hm-2,而经N1、N2、N3处理后,其年凋落物量分别为2238.10、2286.66和2599.50kg.hm-2。表明高氮(N3)处理显著增加了杉木林凋落物量(P<0.05),而中低氮处理(N1、N2)没有显著影响。各处理的总凋落物量表现出明显的季节动态,在2、5和7月出现3个比较明显的峰值。在凋落物的组成中,落叶占总凋落量的70.49%～73.67%,其次分别为落枝(19.38%～20.39%)、碎屑物(4.98%～7.70%)、落果(1.11%～2.16%)和树皮(0.29%～0.33%)。LSD多重比较显示,N3处理对落叶和落果产生显著影响,对其它组分的影响不明显。     

不同林龄杉木组织迁移养分的再利用

为了清楚了解不同林龄杉木(Cunninghamia lanceolata)组织迁移养分(氮、磷、钾、钙、镁)再利用特征, 为人工林丰产的经营管理提供科学依据, 该文利用湖南会同杉木林不同林龄段的活的枝叶与枯死枝叶养分浓度及其差异和枝叶枯死量, 估算枝叶枯死前的养分迁移量。用某林龄段开始和结束时的杉木器官的养分浓度差异, 估算那些在某林龄段开始前林分生产的, 在林龄段结束时仍存活的器官(干、皮、枝、叶、根), 即仍存活物质, 在该林龄段的养分迁移量。将枝叶枯死前迁移的养分和这些仍存活物质中转移的养分与从土壤中吸收的养分相结合, 根据森林生产的生物量, 综合分析森林物质生产的养分利用特征。研究表明: 1-7年生林分, 利用枝叶枯死前迁移的养分生产的生物量及占总生产生物量的比例, 分别为217 kg·hm ^-2·a ^-1和3.52%; 20-25年生林分则分别上升到2 540 kg·hm ^-2·a ^-1和17.50%。枝叶枯死前迁移的养分生产的生物量及占总生产生物量的比例都随林龄增加而增大。林分在12-16、17-20、21-25年林龄段, 由这些仍存活物质中迁移出的养分生产的生物量分别为385、561和450 kg·hm ^-2·a ^-1, 分别占总生产生物量的3.40%、3.40%和3.11%。这些仍存活物质中迁移出的养分量随林龄增加呈现先上升后下降的变化, 由这些养分生产的物质量占总生产物质量的比例随林龄增加呈下降趋势。结果显示, 只要有枝叶枯死发生, 就有枝叶枯死前迁移出养分用于物质再生产。林分郁闭后, 才会发生这些仍存活物质中迁移出的养分再利用。杉木体内养分再分配及贮备机制、杉木生长规律和不同生长发育阶段对养分的需求和利用效率等, 共同调节控制着枝叶枯死前迁移的和这些仍存活物质中迁移出的养分再利用的年变化。     

Aims

To explore the effects of neighbor competition on photosynthetic characteristics in needles and biomass accumulation and allocation of Chinese fir (Cunninghamia lanceolata) seedlings under low phosphorus (P) environment, and to investigate the complex adaptive responses of Chinese fir to available P limitation and intraspecific competition.     

杉木人工林凋落物分解对氮沉降的响应

凋落物分解是陆地生态系统养分循环的关键过程,是全球碳（C）收支的一个重要主要组成部分,正受到全球大气氮（N）沉降的深刻影响。探讨大气氮沉降条件下森林凋落物的分解,有利于揭示森林生态系统C平衡和养分循环对全球变化的响应。选择福建沙县官庄林场1992年栽种的杉木（Cunninghamia lanceolata）人工林为研究对象,自2004年开始野外模拟氮沉降试验,至今12年。氮沉降处理分4个水平,N0、N1、N2和N3分别为0、60、120、240 kg N hm^-2 a^-1。2015年12月开展分解袋试验,对经过氮沉降处理12年的凋落物（叶、枝、果）进行模拟原位分解,每3个月收回一次分解袋样品,为期2年,同时测定凋落物干物质残留量及其C、N和磷（P）含量。结果表明,经2年分解后,氮沉降条件下凋落物叶、枝和果的干物质残留率平均值分别为27.68%、47.02%和43.18%,说明分解速率大小依次为叶 > 果 > 枝。凋落物叶、枝和果的分解系数平均为0.588、0.389和0.455,周转期（分解95%年限）分别为4-5年、6-8年和5-7年。低-中氮处理（N1和N2）均促进凋落物叶、枝和果的分解,以N1的效果更明显,而N3起到抑制作用。N1处理的凋落物叶、枝和果的周转期分别为：4.50年、6.09年和5.85年,N2处理的分别为4.95年、8.16年和6.19年。模拟氮沉降在一定程度上增加了凋落物叶、枝和果分解过程中的N和P含量,但降低了C含量。凋落物叶、枝和果分解过程中C元素呈现释放-富集-释放模式,N和P元素呈现释放与富集交替,除枝的N元素外,其他均表现为释放量大于富集量。     

Seasonal dynamics of active soil organic carbon in four subtropical forests in Southern China

Aims The objective of this paper was to quantify the seasonal variation of active soil organic carbon in the subtropical forests for better understanding of the underline mechanisms in controlling soil organic carbon storage and dynamics in natural and restored forests in the region. Methods The study was conducted in a one-hectare permanent plot at Dashanchong Forest Park in Changsha County, Hunan Province, China. Four types of subtropical forests were selected as our study sites: (1) Cunninghamia lanceolata plantation, (2) Pinus massoniana-Lithocarpus glaber mixed forest, (3) Choerospondias axillaries deciduous broad-leaved forest, and (4) L. glaber-Cyclobalanopsis glauca evergreen broad-leaved forest. The soil samples were taken from 0-15 cm and 15-30 cm depths within each of the forests from December 2011 to September 2012. Soil microbial biomass carbon (MBC), mineralized organic carbon (MOC), readily oxidized carbon (ROC), and dissolved organic carbon (DOC) were analyzed for their seasonal changes. Important findings There existed a considerable seasonal variations of soil MBC, MOC, ROC, DOC among the forests, with a similar patterns of active organic carbon fraction. Soil MBC, MOC and ROC were significantly higher in the summer and the autumn than those in the spring and winter, while soil DOC was higher in the spring, summer and winter than that in the autumn. The seasonal variations of different active organic carbon fractions appeared different within the same forest type. Significantly-positive correlations were found between soil MBC, MOC, ROC, DOC and soil moisture content, soil organic carbon (SOC), total N, hydrolysis N, total P (except for MBC, MOC and ROC in Cunninghamia lanceolata plantation), available P, but not between soil MBC, MOC, ROC, DOC concentrations and soil pH, total K and available K. The results indicated that the differences of exogenous carbon devotion, physicochemical properties were responsible for the significant differences of soil active organic carbon, and the growth rhythm of tree species, soil moisture content, the availability of nutrient (SOC, N and P), and the sources of soil active organic carbon fractions made a major contribution to seasonal variations of soil active organic carbon. Soil MBC, MOC, ROC, and DOC could be used as sensitivity indexes to assess the dynamics of soil C, N and P.     

Responses and regulation mechanisms of microbial decomposers to substrate carbon,nitrogen, and phosphorus stoichiometry

The survival and growth strategies, community structure and functions of microbial decomposers vary with substrate stoichiometry, which profoundly influences substrate decomposition, turnover, and hence the carbon and nutrient cycles of terrestrial ecosystems. It is crucial to understand the relationships among microbial metabolism, community structure and ecosystem processes of terrestrial ecosystems and their responses and feedbacks to global changes. In this review, we first introduced the significance of microbial decomposers in the carbon, nitrogen, and phosphorus cycles of terrestrial ecosystems from perspectives of ecological stoichiometry and metabolic theories. Then we synthesized four potential mechanisms of microbial response and control on substrate stoichiometric variations, i.e., through (1) modifying microbial stoichiometry, (2) shifting microbial community structure, (3) producing extracellular enzymes to acquire limiting resources, and (4) changing microbial carbon, nitrogen, and phosphor use efficiencies. Finally, we proposed three research directions in this field: (1) to comprehensively explore various microbial mechanisms in response to changes in substrate stoichiometry and the relative importance of these mechanisms; (2) to examine influences of global changes on microbial-driven cycles of carbon, nitrogen, and phosphorus; and (3) to explore spatiotemporal changes in the strategies of microbial adaptation to changes in the substrate stoichiometry.     

Convergent responses of nitrogen and phosphorus resorption to nitrogen inputs in a semiarid grassland

Human activities have significantly altered nitrogen (N) availability in most terrestrial ecosystems, with consequences for community composition and ecosystem functioning. Although studies of how changes in N availability affect biodiversity and community composition are relatively common, much less remains known about the effects of N inputs on the coupled biogeochemical cycling of N and phosphorus (P), and still fewer data exist regarding how increased N inputs affect the internal cycling of these two elements in plants. Nutrient resorption is an important driver of plant nutrient economies and of the quality of litter plants produce. Accordingly, resorption patterns have marked ecological implications for plant population and community fitness, as well as for ecosystem nutrient cycling. In a semiarid grassland in northern China, we studied the effects of a wide range of N inputs on foliar nutrient resorption of two dominant grasses, Leymus chinensis and Stipa grandis. After 4 years of treatments, N and P availability in soil and N and P concentrations in green and senesced grass leaves increased with increasing rates of N addition. Foliar N and P resorption significantly decreased along the N addition gradient, implying a resorption‐mediated, positive plant–soil feedback induced by N inputs. Furthermore, N : P resorption ratios were negatively correlated with the rates of N addition, indicating the sensitivity of plant N and P stoichiometry to N inputs. Taken together, the results demonstrate that N additions accelerate ecosystem uptake and turnover of both N and P in the temperate steppe and that N and P cycles are coupled in dynamic ways. The convergence of N and P resorption in response to N inputs emphasizes the importance of nutrient resorption as a pathway by which plants and ecosystems adjust in the face of increasing N availability.     

亚热带杉木（Cunninghamia lanceolata）人工林生长与土壤养分对氮沉降的响应

为探讨亚热带森林对氮沉降增加的响应,项目在杉木人工林中开展了野外模拟N沉降试验,分N0(对照)、N1、N2、N3等4种处理,N沉降量分别为0、60、120、240(kgNhm-2a-1)。通过3a的研究发现,中高氮处理(N2、N3)明显促进了杉木胸径的生长,而低氮处理(N1)则没有产生明显影响。氮沉降对树高生长也有明显的促进作用,但随着氮沉降水平的增加其影响有减弱趋势。通过各水平N处理后,杉木年平均蓄积增长量分别为28.82、28.96、32.63m3hm-2和33.68m3hm-2,表明N沉降在一定程度上增加了林分蓄积量的积累,但处理之间的差异没有达到统计上的显著性水平。随着氮沉降水平的增加,NH4 -N和NO3--N含量明显上升,而土壤pH值、有机质、速效P、速效K和交换性Ca、Mg含量则呈下降趋势。杉木针叶养分状况对氮沉降的响应也比较敏感,N1、N2、N3处理使针叶平均N含量分别增加18.25%、11.68%和13.14%,但对P、K、Ca、Mg含量表现出一定的抑制作用。     

Carbon,nitrogen and phosphorus stoichiometry in leaves and fine roots of dominant plants in Horqin Sandy Land

Aims The stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) in plant organism is vital to understand plant adaptation to environment. In particular, the correlations of elemental stoichiometric characteristics between leaf and fine root could provide insights into the interaction and balance among the plant elements, nutrient use strategies and plant response to global change.Methods We measured C, N, P contents and C:N, C:P, N:P in leaves and fine roots of 60 dominant plants in Horqin sandy land. The 60 plant species were classified into five life forms and two categories such as perennial forb, annual forb, perennial grass, annual grass, shrub, legume, and non-legume. We statistically analyzed the differences and correlations of C, N and P stoichiometry either between fine root and leaf or among five life forms.Important findings The average C, N and P concentrations in leaves of 60 plant species in Horqin sandy land are 424.20 mg·g^-1, 25.60 mg·g^-1 and 2.10 mg·g^-1, respectively. In fine roots, the corresponding element concentrations are 434.03 mg·g^-1, 13.54 mg·g^-1, 1.13 mg·g^-1. N and P concentrations in leaf are approximately twice as high as averages in fine root. Furthermore, similar N:P between leaf and fine root indicates conservative characteristic of elemental stoichiometry in plant organism, suggesting that nutrients distribution is proportional between aboveground and underground of plants. There are significant difference of C, N, P, C:N, C:P and N:P in leaf and root among five life forms. N and P in forb and C:N and C:P in grass are averagely higher than those in other life forms. N:P in annual forb and grass, however, are lower than those in other life forms. C, N in legume are higher than those in non-legume, while C:N in legume is lower than in non-legume. These results imply that nutrient use strategies are significantly different among plant life forms. Correlations analysis showed that N and P in leaf or fine root positively correlated, but C and N, C and P in fine root negatively correlated, suggesting coupling relationship among C, N and P in leaf and fine root. Subsequently, we detected positively significant correlations in C, N, P and their ratios between leaf and fine root, suggesting proportional distribution of photosynthate and nutrient between aboveground and underground during plant growth. Generally, these results supplied fundamental data to understand mass turnover and nutrients cycling of leaves and roots in sand land.     

模拟氮沉降和灌草去除对杉木人工林地土壤微生物群落结构的影响

土壤微生物是陆地生态系统重要的分解者和地上-地下相互作用的纽带。本文以亚热带杉木(Cunninghamia lanceolateata)人工林为对象, 通过模拟林冠层氮沉降和林下灌草去除, 设置4种处理, 包括: 对照(CK)、灌草去除(UR)、氮沉降(N)和氮沉降加灌草去除(N × UR)的野外控制实验, 研究土壤微生物群落结构的响应。本实验分别于2016年4月(春季)和10月(秋季)采集0-10 cm层土壤样品, 运用磷脂脂肪酸法(PLFAs)分析土壤微生物群落结构。结果表明: (1) 10月份土壤微生物总PLFAs量及其他类群土壤微生物PLFAs量显著高于4月份(P < 0.05), 真菌/细菌比值没有显著差异。土壤微生物PLFAs中细菌占优势, 其次为真菌, 放线菌的占比最小; (2)相比CK处理, UR处理下土壤微生物总PLFAs量、细菌PLFAs量、革兰氏阴性菌PLFAs量和放线菌PLFAs量有增加趋势, 但未达到显著差异水平(P > 0.05); (3)相对CK, UR、N和N × UR处理降低了4月份土壤微生物多样性(H°)和均匀度指数(J), 但提高了10月份土壤微生物多样性指数; (4)冗余分析表明, 土壤硝态氮和总磷含量与土壤微生物群落之间呈现显著相关。本研究表明土壤微生物PLFAs在各处理下都表现出明显的季节动态; 短期内林下灌草去除对土壤微生物PLFAs影响表现出一定的促进作用, 氮沉降对土壤微生物群落影响还不甚明显, 需要长期的监测研究来评估两者及其交互作用对土壤微生物群落及其功能的影响。     

Global forest carbon uptake due to nitrogen and phosphorus deposition from 1850 to 2100

Spatial patterns and temporal trends of nitrogen (N) and phosphorus (P) deposition are important for quantifying their impact on forest carbon (C) uptake. In a first step, we modeled historical and future change in the global distributions of the atmospheric deposition of N and P from the dry and wet deposition of aerosols and gases containing N and P. Future projections were compared between two scenarios with contrasting aerosol emissions. Modeled fields of N and P deposition and P concentration were evaluated using globally distributed in situ measurements. N deposition peaked around 1990 in European forests and around 2010 in East Asian forests, and both increased sevenfold relative to 1850. P deposition peaked around 2010 in South Asian forests and increased 3.5‐fold relative to 1850. In a second step, we estimated the change in C storage in forests due to the fertilization by deposited N and P (?C_{ν dep}), based on the retention of deposited nutrients, their allocation within plants, and C:N and C:P stoichiometry. ?C_{ν dep} for 1997–2013 was estimated to be 0.27 ± 0.13 Pg C year^?1 from N and 0.054 ± 0.10 Pg C year^?1 from P, contributing 9% and 2% of the terrestrial C sink, respectively. Sensitivity tests show that uncertainty of ?C_{ν dep} was larger from P than from N, mainly due to uncertainty in the fraction of deposited P that is fixed by soil. ?C_{P dep} was exceeded by ?C_{N dep} over 1960–2007 in a large area of East Asian and West European forests due to a faster growth in N deposition than P. Our results suggest a significant contribution of anthropogenic P deposition to C storage, and additional sources of N are needed to support C storage by P in some Asian tropical forests where the deposition rate increased even faster for P than for N.