Yajuan Xing

Annual soil CO2 efflux in a cold temperate forest in northeastern China: effects of winter snowpack and artificial nitrogen deposition.

We conducted a snow depth 0 cm (non-snowpack), 10 cm, 20 cm, 30 cm and natural depth) gradient experiment under four quantities of nitrogen addition (control, no added N; low-N, 5 g N m−2 yr−1; medium-N, 10 g N m−2 yr−1; and high-N, 15 g N m−2 yr−1) and took an-entire-year measurements of soil respiration (Rs) in Korean pine forests in northeastern China during 2013–2014. No evidence for effects of N on Rs could be found during the growing season. On the other hand, reduction of snowpack decreased winter soil respiration due to accompanied relatively lower soil temperature. We found that winter temperature sensitivities (Q10) of Rs were significantly higher than the growing season Q10 under all the N addition treatments. Moderate quantities of N addition (low-N and medium-N) significantly increased temperature sensitivities (Q10) of Rs, but excessive (high-N) addition decreased it during winter. The Gamma empirical model predicted that winter Rs under the four N addition treatments contributed 4.8. ± 0.3% (control), 3.6 ± 0.6% (low-N), 4.3 ± 0.4% (medium-N) and 6.4 ± 0.5% (high-N) to the whole year Rs. Our results demonstrate that N deposition will alter Q10 of winter Rs. Moreover, winter Rs may contribute very few to annual Rs budget.

Nitrogen deposition may enhance soil carbon storage via change of soil respiration dynamic during a spring freeze-thaw cycle period

As crucial terrestrial ecosystems, temperate forests play an important role in global soil carbon dioxide flux, and this process can be sensitive to atmospheric nitrogen deposition. It is often reported that the nitrogen addition induces a change in soil carbon dioxide emission in growing season. However, the important effects of interactions between nitrogen deposition and the freeze-thaw-cycle have never been investigated. Here we show nitrogen deposition delays spikes of soil respiration and weaken soil respiration. We found the nitrogen addition, time and nitrogen addition×time exerted the negative impact on the soil respiration of spring freeze-thaw periods due to delay of spikes and inhibition of soil respiration (p < 0.001). The values of soil respiration were decreased by 6% (low-nitrogen), 39% (medium-nitrogen) and 36% (high-nitrogen) compared with the control. And the decrease values of soil respiration under medium- and high-nitrogen treatments during spring freeze-thaw-cycle period in temperate forest would be approximately equivalent to 1% of global annual C emissions. Therefore, we show interactions between nitrogen deposition and freeze-thaw-cycle in temperate forest ecosystems are important to predict global carbon emissions and sequestrations. We anticipate our finding to be a starting point for more sophisticated prediction of soil respirations in temperate forests ecosystems.

Relationship between Diversity of Forest Plant and Community Dynamics in Eastern Mountain Area of Heilongjiang Province, China

The biodiversity was studied in 26 communities with different structures tructures in Maoershan National Park and Liangshui Natural Reserve of Northeast Forestry University in Heilongjiang Province, China. Composition index (CI) was taken as a parameter to quantify the community dynamics, which can nicely describe forest community dynamics, meanwhile, the relationship between diversity and community dynamics were also investigated and analyzed. Results showed that the total number species of community, richness, evenness, and Shannon-Wiener diversity index were obviously different in every community. The richness decreased with the increasing CI of every community, which means richness was in inverse proportion to community dynamics. The Shannon-Wiener index of every community increased from the initial stage to the middle stage of succession, and then decreased in the climax stage. The coverage weighted foliage-height diversity index increased along with the increase of CI, which was similar as the pattern diversity.

Nitrogen deposition and decreased precipitation does not change total nitrogen uptake in a temperate forest

Decreased precipitation and increased anthropogenical by derived nitrogen (N) are important climate change factors that alter the availability of soil water and N which are crucial to root function and morphological traits. However, these factors are seldom explored in forests. To clarify how altered precipitation and N addition affect the uptake of organic and inorganic N by fine roots, a field hydroponic experiment using brief 15N exposures was conducted in a temperate forest in northern China. The root traits related to nutrient foraging (root morphology and mycorrhizal colonization) were measured simultaneously. Our results showed that all three tree species preferred ammonium (NH4+) over glycine and nitrate (NO3-), and NH4+ contributed 73% to the total N uptake from the soil. Uptake of glycine was higher than that of NO3-. Decreased precipitation, N addition, and their interaction increased NH4+ uptake rate compared with the control. Decreased precipitation decreased the glycine and NO3- uptake rate. Moreover, N addition, decreased precipitation and their interaction changed root morphological traits and significantly decreased mycorrhizal colonization. Although our treatments resulted in changes to the root traits and the forms of N uptake by plants, the total amount of N uptake did not change among all treatments. We conclude that although fine root traits of dominant tree species in temperate forests have high plasticity in response to climate change, nutrient balance in plants causes the total amount of N uptake to remain unchanged.

Responses and mechanisms of soil greenhouse gas fluxes to changes in precipitation intensity and duration: a meta-analysis for a global perspective

Abstract: Although extensive manipulative experiments have been conducted to study the effects of altered precipitation intensity and duration on soil greenhouse gas (GHG; carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)) fluxes, the general patterns of GHGs to altered precipitation have not been globally described across biomes. Thus, we performed a meta-analysis of 84 published studies to examine the general responses of CO2, CH4, and N2O fluxes to altered precipitation. Our results indicated that increased precipitation significantly increased N2O emissions (+154.0%) and CO2 fluxes (+112.2%) and significantly decreased CH4 uptake (-41.4%); decreased precipitation significantly decreased N2O emissions (-64.7%) and CO2 fluxes (-8.6%) and significantly increased CH4 uptake (+32.4%). Moreover, increased precipitation significantly increased litter biomass and microbial biomass and decreased root biomass and the root:shoot ratio. However, decreased precipitation significantly decreased litter biomass and root biomass and significantly increased root:shoot ratio. These results suggest that precipitation changes could alter the carbon distribution patterns in plants. In addition, the CO2, CH4, and N2O fluxes exhibited diverse responses to different ecosystems, durations of precipitation changes, and changes in precipitation intensity. These results demonstrate that there are many factors that regulate the responses of GHG to precipitation changes.

Nutrient Exports Under Different Harvesting Regimes in Two Types of Larch Plantation with Different Age in Northeastern China

It has been confirmed in studies conducted in different regions and forest types that the harvesting regime has a significant impact on the export of nutrients from a plantation. Through establishing allometric growth equations and studying nutrient distribution patterns, the amounts of nutrients exported from larch (Larix spp.) plantations with different stand ages under different harvesting regimes (removal of stem wood, branches and bark (Rsbb), removal of stem wood and bark (Rsb), and removal of stem wood (Rs)) were determined in the present study. The results showed the following: 1) the organs of 20-year-old and 40-year-old larch trees exhibited basically the same nutrient distribution pattern. However, due to the difference in biomass partitioning in trees of these ages, they showed a significant difference in the cumulative amounts of nutrients in their organs. Specifically, the cumulative amounts of nutrient elements in the leaves and old branches of 20-year-old larch trees were significantly higher than in 40-year-old larch trees. However, the cumulative amounts of various nutrients in the xylem of the trunks of 20-year-old larch trees were significantly lower than in 40-year-old larch trees. 2) Compared with the Rsbb20, Rsbb40 or Rsb20 could result in significant decreases in the annual mean amounts of nutrients exported, the ratio of the annual mean total amount of nutrients exported to the annual net cumulative total amount of nutrients and the proportion of soil nutrients in the 0-30 cm soil layer. Changing the Rsbb20 to an Rsb40 or an Rs40 could further reduce the annual mean amounts of nutrients exported, the ratio of the annual mean total amount of nutrients exported to the annual net cumulative total amount of nutrients and the proportion of soil nutrients in the 0-30 cm soil layer. 3) Among the examined harvesting regimes, the Rs20 resulted in the lowest annual mean amounts of nutrients being exported. However, there was no significant difference in the annual mean amounts of nutrients exported between the Rs20 and the Rs40. The amounts of N, Ca and Mg exported under the Rs20 were slightly higher than under the Rs40, whereas the amounts of P and K exported under the Rs20 were slightly lower than under the Rs40. Hence, the harvesting regime is an important factor that results in the export of system nutrients and a decline in soil fertility. Therefore, prolonging the harvesting cycle and adopting Rs are two options for reducing the nutrients export.