Comparative assessment of soil fertility across varying elevations

Species mixing enhances the resistance of Robinia pseudoacacia L. to drought events in semi-arid regions: Evidence from China's Loess Plateau.

In order to elucidate the adaptation mechanisms of the stoichiometric characteristics of Abies georgei var. smithii in southeastern Tibet to different habitats, the spatial and temporal dynamics of the nutrient contents and stoichiometric ratios among the leaf, branch, stem, and root organs were analyzed on Sejila Mountain in southeastern Tibet at different elevations (3500 m, 3900 m, and 4300 m). The results show that (1) the C and K contents of the fir organs did not change significantly with increasing elevation in the same season, while the N and P contents showed an overall increasing trend with increasing elevation, with the C and N contents being the highest in the leaves. The distribution order was leaves > branches > roots > stem; the P and K content order in each organ was branches > leaves > roots > stem. (2) At the same elevation and in different seasons, the Abies georgei var. smithii organs showed a similar convergence in terms of nutrient storage and utilization strategies, and more nutrients were optimally allocated between the assimilated and stored organs in the alpine habitats, which represents a “trade-off” strategy. (3) Compared to the findings of the global-scale studies, this study area has low N, P, and K contents, and its growth is limited by both N and P. Due to physiological and nutrient balance constraints, the content of the N-limited elements in the plants is relatively stable, which is in line with the “limiting element stability hypothesis”. (4) Principal component analysis showed that the influence of environmental factors on the stoichiometric characteristics of the different organs of Abies georgei var. smithii had a spatial scale effect, and that Abies georgei var. smithii demonstrated increased accumulation of N and P contents when subjected to environmental stress, which promoted the domestication and adaptation of the plant, enabling it to show good nutrient accumulation capacity and good adaptation strategies even at high elevation; thus, it has become a pioneer tree species at high elevations. This research work shows that the resilient adaptation of Abies georgei var. smithiir to environmental change has led to differences in the nutrient uptake and use efficiency and the adaptation patterns of the organs at different altitudinal gradients, with each organ adapting to habitat changes by adjusting its nutrient storage strategy between habitats.

/pdf/stoichiometric-characteristics-of-abies-georgei-var-smithii-2zk04ouh.pdf

Stoichiometric Characteristics of Abies georgei var. smithii Plants in Southeast Tibet

Phosphorus (P) fertilizer is commonly used in subtropical plantations to augment nutrients including carbon (C), nitrogen (N), and P to maintain plants engaged in metabolism. Stoichiometric homeostasis reflects the adaptation of plants to various environments (including P fertilizer supply rates). It is thus of great significance to understand C:N:P stoichiometry in the plant–litter–soil system under P addition and the stoichiometric homeostasis of plant tissues for the P fertilization management of slash pine (Pinus elliottii Engelm) plantations. In subtropical China, we measured the C, N, and P contents in root, branch, needle, litter, and soil in slash pine plantations fertilized with four treatments, P1 (25 kg P ha1 yr1), P2 (50 kg P ha1 yr1), P3 (100 kg P ha1 yr1), and a control (CK), and calculated the stoichiometric homeostasis of plant tissues. The results show that P3 treatment increased the C, N, and P contents of the needle. P2 and P3 treatments increased the P content of the litter and the N:P ratio of the root while decreasing the C:N ratio of the root. P addition treatments increased C and P element accumulation in soil but had no effect on soil stoichiometry. The nutrient contents of needle and branch were higher than those of root and litter, indicating that slash pine was more inclined to allocate nutrients to the aboveground tissues. The stoichiometric homeostasis of C, N, and P among plant tissues was graded as follows: root > branch > needle. The needle’s nutritional homeostasis was C > N > P, with 1/H values of 0.08, 0.34, and 0.74, respectively. These findings demonstrate that during P addition, the C, N, and P stoichiometric homeostasis varied among plant tissues and element types. In conclusion, P application altered nutrient distribution in the plant–litter–soil system, alleviating P restriction in slash pine forests in southern China. P addition levels should be finely adjusted in the future for longer-term observation trials, and the trade-off between P addition rates and economic and ecological advantages should be properly examined.

/pdf/response-of-c-n-p-stoichiometry-to-phosphorus-addition-and-2hd4amg2.pdf

Response of C:N:P Stoichiometry to Phosphorus Addition and Homeostasis of Plant Tissues in a Subtropical Slash Pine Plantation

An aircraft mounted laser communications system is being developed for an air to air communication experiment to be performed over a range of 50 to 500 kilometers at altitudes up to 40,000 feet. The purpose of the experiment is to demonstrate and characterize communication between two aircraft at various ranges, altitudes and atmospheric conditions. Communication data rates are up to 1 GBPS using four on-off keyed 810 nm diode lasers multiplexed into two circularly polarized transmitting apertures. The communication receiver uses a 134 mm diameter Matsutov telescope with APD's for the detectors. Two separate beacon lasers at 852 nm provide sources for tracking. Two T-39 aircraft each will be equipped with a laser communication system and experimental data collection equipment.

500 kilometer 1 GBPS airborne laser link

Response of plant, litter, and soil C:N:P stoichiometry to growth stages in Quercus secondary forests on the Loess Plateau, China

Adopting beacon in the spatial optical communication between movement platforms is an important method of finishing the acquisition and tracking course. A newly beacon tracking servo system in spatial optical communication is designed with double DSPs, Kalman model is adopted to forecast target. The design of hardware and software system is introduced in detail, the acquisition time of beacon is perfectly presented from different experimental conditions, and the scan error time of beacon is also analysed at length. According to experimental result, the system has the characteristics of high precision, quick scan and real-time, and it is beneficial for the system to apply in optical communication between the spatial movement platforms.

Simulation experiment of acquisition & tracking with beacon between the spatial movement platforms

Biomass Difference between Monocultures and Mixed Plantations and its Influencing Factors: A Meta-Analysis

The southern mountainous areas in Ningxia are representative regions of the Loess Plateau, with extremely fragile ecological environment. Large area of pure plantations established during the project of Grain for Green has suffered from poor nutrient availability and biodiversity loss, while planting mixed plantations is commonly consi-dered as an effective way to improve the ecological benefits. We selected Robinia pseudoacacia + Picea asperata mixed plantation, R. pseudoacacia + Armeniaca sibirica mixed plantation, A. sibirica pure plantation and R. pseudoa-cacia pure plantation located ina Ningnan mountainous area as test objects. Based on the theory and method of ecological stoichiometry, we measured the C, N and P contents of leaves, litter and fine roots to understand nutrient cycling characteristics of different plantations. The results showed that there was significant difference in foliar stoichiometry of each tree species within the four plantations. P. asperata leaves had the highest C content in the R. pseudoacacia + P. asperata mixed plantation, and R. pseudoacacia leaves had the highest N and P contents in the R. pseudoacacia + A. sibirica mixed plantation. N content of R. pseudoacacia and A. sibirica leaves was significantly higher in mixed plantation compared with that in pure plantation. There was no significant difference in litter biomass, litter C, N, P contents and stoichiometric ratios between the pure and mixed plantations of R. pseudoacacia. Litter biomass in A. sibirica pure plantation was significantly higher than that in R. pseudoacacia + A. sibirica mixed plantation, while litter C content was significantly lower than that in the mixed plantation. Fine root biomass decreased with increasing soil depth in the four plantations, with total fine root biomass being the highest in the R. pseudoacacia + A. sibirica mixed plantation. N content and N:P of fine roots in the R. pseudoacacia + A. sibirica mixed plantation were higher than those in R. pseudoacacia and A. sibirica pure plantations. There was significant negative correlation between N content in leaves and fine roots of R. pseudoacacia + A. sibirica mixed plantation. There were significant negative correlations between the N content of leaves and litter, as well as between the P content of leaves and fine roots in the R. pseudoacacia + P. asperata mixed plantation. P content between litter and fine roots in A. sibirica pure plantation was significantly negatively correlated. Nutrient status of mixed plantations was better than pure plantations in the Ningnan mountainous area, with the mixed plantation of R. pseudoacacia and A. sibirica being the best. Mixed planting reduced nutrient limitation on plant growth to a certain extent.

Ecological stoichiometry of leaf-litter-fine roots in mixed plantations in mountainous area of Southern Ningxia, China.

Establishing mixed‐species plantations has become the most promising planting method to provide various goods and improve multiple environmental services. Although mixed planting has the potential to increase tree biomass, the divergent findings make it challenging to understand the mixing effects on whole forest (trees, shrubs, herbs, and litter) biomass. Therefore, we conducted a meta‐analysis compiling 156 studies published from 1982 to 2021 across 128 sites in China. We aimed to quantify the mixing effects on forest biomass between mixed plantations and monocultures and disentangle the driving factors. Our results showed that mixed planting significantly increased the total biomass, biomass of tree, and shrub layer by 14.07%, 22.49%, and 34.84%, respectively, when compared with monocultures. The effects of mixed planting on biomass were more pronounced in plantations with both nitrogen‐fixing trees and non‐nitrogen‐fixing trees, plantations with both coniferous and broad‐leaved trees, as well as uneven‐aged plantations containing young‐ and middle‐aged species. Furthermore, our results demonstrated the effects of mixed planting were predominantly governed by climatic conditions and woodland characteristics. The effect size of total biomass exhibited a significant positive correlation with mean annual temperature and precipitation, while the shrub and herb layers showed a significant negative relationship with these climatic variables. Our findings highlighted the importance of complementarity effects in mixed plantations, especially establishing uneven‐aged plantations with different leaf morphology types and N acquisition strategies. Overall, our meta‐analysis could provide strategies for future sustainable ecosystem management and improving the terrestrial carbon sink.

Biomass difference between mixed plantations and monocultures and its influencing factors: A meta‐analysis

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