[Response of Soil Respiration Rates to Soil Temperature and Moisture at Different Soil Depths of Caragana korshinskii Plantation in the Loess-Hilly Region].

It is of great significance to clarify the influence of soil temperature and moisture on soil respiration rate and its characteristics in ecologically fragile regions under the background of climate change for the accurate assessment and prediction of carbon budgets in this region. The average CO2 concentration and soil temperature and moisture at different soil depths (10, 50, and 100 cm) were measured using a CO2 analyzer and temperature and moisture sensors. The soil respiration rate was calculated using Fick's first diffusion coefficient method. The dynamic characteristics of soil temperature, soil moisture, and soil respiration rate in different soil depths were explored, and the response of soil respiration rate to soil temperature and moisture were further analyzed. The results showed that the diurnal variation in soil respiration rate decreased significantly with the increase in soil depth (P<0.05), and the peak time lagged behind. Soil respiration rate in adjacent soil depths (10, 50, and 100 cm) lagged 1 h from top to bottom. The monthly variation in soil respiration rate was a multi-peak curve, in which the maximum soil respiration rates of 10, 50, and 100 cm soil depths were on July 25th, August 6th, and August 10th, reaching 13.96, 2.96, and 1.47 µmol·(m2·s)-1, respectively. The effect of soil temperature on soil respiration rate decreased with the increase in soil depth. Soil temperature at 50 cm and below had no significant effect on soil respiration rate (P>0.05). The fitting index of 10 cm soil depth was the best (R2=0.96), but the fitting indexes of 50 cm and 100 cm soil depths were poor (R2=0.00 and R2=0.01, respectively). The temperature sensitivity coefficient Q10 decreased with the increase in soil depth. Soil moisture in different soil depths had significant effects on soil respiration rate (P<0.05), and the quadratic fitting indicated that 50 cm (R2=0.35)>10 cm (R2=0.22)>100 cm (R2=0.31). The combined effects of soil temperature and moisture in different soil depths could explain 96%, 6%-50%, and 22%-24% of soil respiration rate, respectively. In summary, the effects of soil temperature and moisture at different soil depths of the Caragana korshinskii plantation in the loess-hilly region on soil respiration rate differed. The soil respiration rate of the 10 cm soil depth was affected by the comprehensive effect of soil temperature and moisture; however, the relative contribution of soil temperature was higher, and soil moisture at and below a soil depth of 50 cm was the key factor. These results could help improve predictions on the impact of future climate change on the carbon cycle of terrestrial ecosystems in the region and provide a theoretical basis for greenhouse gas regulation in the future.

[Responses of productivity of typical natural secondary forests and plantations to climate change in Shaanxi Province, China]. / é™•è¥¿çœå ¸åž‹å¤©ç„¶æ¬¡ç”Ÿæž—å’Œäººå·¥æž—ç”Ÿäº§åŠ›å¯¹æ°”å€™å˜åŒ–çš„å“åº”.

We analyzed the changes of net primary productivity (NPP) and net ecosystem productivity (NEP) of Quercus spp. forest and Robinia pseudoacacia plantation under different future climate scenarios in Shaanxi Province during 2015-2100, using the process-based dynamic vegetation model-LPJ-GUESS. The results showed that compared with the benchmark period (1961-1990), NPP of Quercus spp. forest and R. pseudoacacia plantation in northern Shaanxi would decrease by 4.9%-29.5% and 22.5%-56.2% respectively, while that in Guanzhong and southern Shaanxi would increase by 13.0%-49.0% and 21.3%-62.9% respectively in the future. The NPP of Quercus spp. forest and R. pseudoacacia plantation under the RCP8.5 scenario was the highest, followed by that under the RCP4.5 and RCP2.6 scenarios. Those two types of forest would be carbon sink in three subregions in the future. Quercus spp. forest would have stronger carbon sink function in nor-thern Shaanxi and Guanzhong, while R. pseudoacacia plantation would have stronger carbon sink function in Southern Shaanxi. Under different RCP scenarios, the NEP variation range of R. pseu-doacacia plantation was greater than that of Quercus spp. forest in three subregions.

[Dynamic change of Pinus tabuliformis forest productivity and its response to future climate change in Shaanxi Province, China.] / 陕西省油松林生产力动态及对未来气候变化的响应.

This study analyzed the dynamics of net primary productivity (NPP) of Pinus tabuliformis forest under future climate scenarios in Shaanxi Province during 2015-2100, using a dynamic vegetation model (LPJ-GUESS). The results showed that in the 2015-2100 period, annual mean temperature of this region would significantly increase by 0.12, 0.23 and 0.54 ℃·10 a-1 under RCP2.6, RCP4.5 and RCP8.5 scenarios, respectively, while the annual precipitation would have no significant change under climate scenarios except RCP4.5, under which it would significantly increase by 14.36 mm·10 a-1. Compared with the NPP of P. tabuliformis forest in the historical period (1961-1990), it would increase by 1.6%-29.6% in the future period, and the enhancement could reach 45.4% at the end of this century (2071-2100) under RCP8.5 scenario. The NPP under the RCP8.5 scenario was the highest, followed by the RCP4.5 and RCP2.6 scenarios. During 2015-2100, the NPP in the northern Shaanxi region would significantly decrease with the rate of 41.00 and 21.00 g C·m-2·10 a-1 under the RCP2.6 and RCP4.5 scenarios, respectively, implying that this area has the potentiality to be carbon source.

[Sap flux density in response to rainfall pulses for Pinus tabuliformis and Hippophae rhamnoides from mixed plantation in hilly Loess Plateau]. / é»„åœŸä¸˜é™µåŒºæ··äº¤æž—ä¸­æ²¹æ¾å’Œæ²™æ£˜æ ‘å¹²æ¶²æµå¯¹é™é›¨è„‰å†²çš„å“åº”.

Thermal dissipation probe (TDP) was used to continuously measure the sap flux density (Fd) of Pinus tabuliformis and Hippophae rhamnoides individuals in hilly Loess Plateau, from June to October 2015, and the environmental factors, i.e., photosynthetic active radiation (PAR), water vapor pressure deficit (VPD), and soil water content (SWC), were simultaneously monitored to clarify the difference of rainfall utilization between the two tree species in a mixed plantation. Using the methods of a Threshold-delay model, stepwise multiple regression analyses, and partial correlation analyses, this paper studied the process of Fd in these two species in response to the rainfall pulses and then determined the effects of environmental factors on Fd. The results showed that, with the increase of rainfall, the response percentages of Fd in both P. tabuliformis and H. rhamnoides increased at first but then decreased; specifically, in the range of 0-1 mm rainfall, the Fd of P. tabuliformis (-16.3%) and H. rhamnoides (-6.3%) clearly decreased; in the range of 1-5 mm rainfall, the Fd of P. tabuliformis decreased (-0.4%), whereas that of H. rhamnoides significantly increased (9.0%). The lower rainfall thresholds (RL) of Fd for P. tabuliformis and H. rhamnoides were 6.4 and 1.9 mm, respectively, with a corresponding time-lag (τ) of 1.96 and 1.67 days. In the pre-rainfall period, the peak time of Fd of P. tabuliformis converged upon 12:00-12:30 (70%), while the Fd of H. rhamnoides peaked twice, between 10:30 and 12:00 (48%) and again between 16:00 and 16:30 (30%). In the post-rainfall period, the peak time of Fd of P. tabuliformis converged upon 11:00-13:00 (40%), while that of H. rhamnoides peaked twice, between 12:00 and 13:00 (52%) and again between 16:30 and 17:00 (24%). Among the environmental factors, the rank order of factors associated with the Fd of both P. tabuliformis and H. rhamnoides was PAR>VPD, before rainfall. However, the rank order of factors influencing the Fd of P. tabuliformis was PAR>VPD>0-20 cm SWC (SWC0-20), whereas this order was different for H. rhamnoides: SWC0-20 >PAR >VPD, after rainfall. This mixed plantation of P. tabuliformis and H. rhamnoides trees had a high stability of water utilization.

[Characteristics and affecting factors of sap flow density of Pinus tabuliformis and Hippophae rhamnoides in growing season in the hilly region of the Loess Plateau, China]. / é»„åœŸä¸˜é™µåŒºæ²¹æ¾ã€æ²™æ£˜ç”Ÿé•¿æ—ºç››æœŸæ ‘å¹²æ¶²æµå¯†åº¦ç‰¹å¾åŠå ¶å½±å“å› ç´ .

The dynamic changes of sap flow density (Js) of Pinus tabuliformis and Hippophae rhamnoides in plantations from July to September in 2015 was monitored through thermal dissipation probe in the hilly region of the Loess Plateau. In addition, plant physiological characteristics were analyzed to determine the water use types of these two species. The results indicated that the daily changes of Js of P. tabuliformis and H. rhamnoides showed a single peak during both pre- and post-precipitation. The Js of P. tabuliformis in growing season (12.62 mL·m-2·s-1) was significantly higher than that of H. rhamnoides (2.60 mL·m-2·s-1). The Js of these two species were significantly positively correlated with photosynthetic active radiation, vapor pressure deficit, soil volume-tric water content (SWC). The Js of these two species were mainly influenced by meteorological factors during pre- and post-precipitation in both August and September. The contribution of SWC to Js of H. rhamnoides increased by 4.2% after precipitation in September, but the contribution of SWC to Js of P. tabuliformis decreased by 0.3% after precipitation in both August and September, respectively. Meanwhile, P. tabuliformis showed significantly higher water potential in midday leaf, but lower coefficient of variation (7.3%) than H. rhamnoides with the coefficient of variation of 11.7%. However, H. rhamnoides exhibited higher leaf stomatal conductance. Thus, P. tabuliformis and H. rhamnoides could be considered as isohydry and anisohydry species, respectively.

[C, N, P stoichiometric characteristics of tree, shrub, herb leaves and litter in forest community of Shaanxi Province, China].

A total of 121 sampling sites were selected to study the C, N, P stoichiometric characteristics among the leaves of tree, shrub, herb and the litter of the majority forest community of Shaanxi Province, China. We also studied their relationships with geographical factors. The results showed that C, N concentrations were highest in tree leaf, P concentration was highest in herb leaf, and the C, N, P concentrations were lowest in litter. Leaf C: N: P ratios of tree, shrub, herb leaves and litter were 439.4:14.2:1, 599.2:13.5:1, 416.5:13.3:1, 504.8:15.5:1, respectively. The N:P ratios of tree, shrub and herb leaves were not significantly different, but they were all significantly higher than that of litter layer, indicating N:P ratio of different living life forms' leaves was stable. Compared with N, C and P had better relationships in each layer, and the relationships of leaf C, N, P stoichiometry between tree and herb leaves were better than those between tree and shrub leaves. The correlations of C, N, P stoichiometry between litter and the tree or herb leaves were highly significantly positive, and the correlations of P stoichiometry between litter and shrub leaves were highly significantly positive. Shrub leaf N, P concentration increased with the increasing latitude, and herb leaf N, P concentrations decreased with the increasing longitude. Compared with the longitude and latitude, the effect of altitude was smaller, and only tree leaf N:P decreased with the increasing latitude. Multivariate linear regression analysis results showed that the influence of geographical factors on herb leaf was longitude > latitude > altitude, while was latitude > longitude > altitude for tree, shrub leaves and litter.

[Storage and allocation of carbon and nitrogen in Pinus tabuliformis plantations on the south slope of the East Qinling Mountains, China].

The objective of this study was to study carbon and nitrogen storages and distributions in Pinus tabuliformis plantations along an age chronosequence of 8-, 25-, 35-, 42- and 61-year-old on the south slope of the East Qinling Mountains; China. Results showed that the carbon content and nitrogen contents ranged from 441.40 to 526.21 g . kg-1 and from 3.13 to 3.99 g . kg-1 in arbor layer, from 426.06 to 447.25 g . kg-1 and from 10.62 to 12.45 g . kg-1 in shrub layer, from 301.37 to 401.52 g . kg-1 and from 10.35 to 13.33 g kg-1 in herb layer, from 382.83 to 424.71 g . kg-1, and from 8.69 to 11.90 g . kg-1 in litter layer, and from 1.51 to 18.17 g . kg-1 and from 0.29 to 1.45 g . kg-1 in soil layer (0-100 cm) , respectively. The largest carbon and nitrogen storages in arbor layer were trunks and branches, which made up 48.5% to 62.7% and 39.2% to 48.4% of the total storage, respectively. Carbon and nitrogen storages of P. tabuliformis plantations were obviously age-dependent. Carbon storage at first increased with stand Age before the stand was ripe. It was the highest (146.06 t . hm-2) when the stand was 35 year-old, after which the carbon storage de- creased. The nitrogen storage reached the peak value of 10.99 t . hm-2 at 25 year-old. The average carbon and nitrogen storages were 45.33 t . hm-2 and 568.55 kg . hm-2 in the plant layer and, 73.12 and 8.57 t . hm-2 in soil layer, respectively. Moreover, carbon and nitrogen were accumulated at higher levels in the surface soil layer. In addition, the storages of carbon and nitrogen were mainly distributed in soil layer and arbor layer in this region. The average carbon storage in different components followed an order as soil layer (64.1%) > arbor layer (30.0%) > shrub-herb and litter layers (5.9%), while the nitrogen storage followed as: soil layer (93.2%) > arbor layer (5.3%) > shrub-herb and litter layers (1.5%).

[Storage and allocation of carbon and nitrogen in Robinia pseudoacacia plantation at different ages in the loess hilly region, China].

The 9-, 17-, 30- and 37-year-old Robinia pseudoacacia plantations in the loess hilly region were investigated to study the dynamics and allocation patterns of carbon and nitrogen storage. The results showed that the ranges of carbon and nitrogen contents were 435.9-493.4 g x kg(-1) and 6.8-21.0 g x kg(-1) in the arbor layer, 396.3-459.2 g x kg(-1) and 14.2-23.5 g x kg(-1) in the herb and litter layer, and 2.7-10.7 g x kg(-1) and 0.2-0.7 g x kg(-1) in the soil layer, respectively. The branch was the major carbon and nitrogen pool in the arbor layer, accounting for 46.9%-63.3% and 39.3%-57.8%, respectively. The maximum storage values were 30.1 and 1.8 Mg x hm(-2) for carbon and nitrogen, respectively, in the 0-20 cm soil layer in the 37-year-old R. pseudoacacia plantation. The total carbon and nitrogen storage in the R. pseudoacacia plantation ecosystem increased with increasing forest age, and the maximum values were 127.9 Mg x hm(-2) and 6512.8 kg x hm(-2) for carbon and nitrogen storage, respectively, in the 37-year-old R. pseudoacacia plantation. Soil layer was the major carbon and nitrogen pool of R. pseudoacacia plantation ecosystem, accounting for 63.3%-83.3% and 80.3%-91.4%, respectively.