Positive effects of night warming on physiology of coniferous trees in late growing season: Leaf and root

Nitrogen availability mediates soil carbon cycling response to climate warming: A meta-analysis

Global climate warming may induce a positive feedback through increasing soil carbon (C) release to the atmosphere. Although warming can affect both C input to and output from soil, direct and convincing evidence illustrating that warming induces a net change in soil C is still lacking. We synthesized the results from field warming experiments at 165 sites across the globe and found that climate warming had no significant effect on soil C stock. On average, warming significantly increased root biomass and soil respiration, but warming effects on root biomass and soil respiration strongly depended on soil nitrogen (N) availability. Under high N availability (soil C:N ratio < 15), warming had no significant effect on root biomass, but promoted the coupling between effect sizes of root biomass and soil C stock. Under relative N limitation (soil C:N ratio > 15), warming significantly enhanced root biomass. However, the enhancement of root biomass did not induce a corresponding C accumulation in soil, possibly because warming promoted microbial CO₂ release that offset the increased root C input. Also, reactive N input alleviated warming-induced C loss from soil, but elevated atmospheric CO₂ or precipitation increase/reduction did not. Together, our findings indicate that the relative availability of soil C to N (i.e., soil C:N ratio) critically mediates warming effects on soil C dynamics, suggesting that its incorporation into C-climate models may improve the prediction of soil C cycling under future global warming scenarios.

Anthropogenic changes to the nighttime environment

How the relative impacts of anthropogenic pressures on the natural environment vary between different taxonomic groups, habitats, and geographic regions is increasingly well established. By contrast, the times of day at which those pressures are most forcefully exerted or have greatest influence are not well understood. The impact on the nighttime environment bears particular scrutiny, given that for practical reasons (e.g., researchers themselves belong to a diurnal species), most studies on the impacts of anthropogenic pressures are conducted during the daytime on organisms that are predominantly day active or in ways that do not differentiate between daytime and nighttime. In the present article, we synthesize the current state of knowledge of impacts of anthropogenic pressures on the nighttime environment, highlighting key findings and examples. The evidence available suggests that the nighttime environment is under intense stress across increasing areas of the world, especially from nighttime pollution, climate change, and overexploitation of resources.

Regulating carbon and water balance as a strategy to cope with warming and drought climate in Cunninghamia lanceolata in southern China

Human activities have increased the possibility of simultaneous warming and drought, which will lead to different carbon (C) allocation and water use strategies in plants. However, there is no conclusive information from previous studies. To explore C and water balance strategies of plants in response to warming and drought, we designed a 4-year experiment that included control (CT), warming (W, with a 5°C increase in temperature), drought (D, with a 50% decrease in precipitation), and warming and drought conditions (WD) to investigate the non-structural carbohydrate (NSC), C and nitrogen (N) stoichiometry, and intrinsic water use efficiency (iWUE) of leaves, roots, and litter of Cunninghamia lanceolata, a major tree species in southern China. We found that W significantly increased NSC and starch in the leaves, and increased NSC and soluble sugar is one of the components of NSC in the roots. D significantly increased leaves' NSC and starch, and increased litter soluble sugar. The NSC of the WD did not change significantly, but the soluble sugar was significantly reduced. The iWUE of leaves increased under D, and surprisingly, W and D significantly increased the iWUE of litter. The iWUE was positively correlated with NSC and soluble sugar. In addition, D significantly increased N at the roots and litter, resulting in a significant decrease in the C/N ratio. The principal component analysis showed that NSC, iWUE, N, and C/N ratio can be used as identifying indicators for C. lanceolata in both warming and drought periods. This study stated that under warming or drought, C. lanceolata would decline in growth to maintain high NSC levels and reduce water loss. Leaves would store starch to improve the resiliency of the aboveground parts, and the roots would increase soluble sugar and N accumulation to conserve water and to help C sequestration in the underground part. At the same time, defoliation was potentially beneficial for maintaining C and water balance. However, when combined with warming and drought, C. lanceolata growth will be limited by C, resulting in decreased NSC. This study provides a new insight into the coping strategies of plants in adapting to warming and drought environments.

Nitric oxide alleviates salt stress through protein S-nitrosylation and transcriptional regulation in tomato seedlings

NO enhances the resistance of tomato seedlings to salt stress through protein S-nitrosylation and transcriptional regulation, which involves the regulation of MAPK signaling and carbohydrate metabolism. Nitric oxide (NO) regulates various physiological and biochemical processes and stress responses in plants. We found that S-nitrosoglutathione (GSNO) treatment significantly promoted the growth of tomato seedling under NaCl stress, indicating that NO plays a positive role in salt stress resistance. Moreover, GSNO pretreatment resulted in an increase of endogenous NO level, S-nitrosothiol (SNO) content, S-nitrosoglutathione reductase (GSNOR) activity and GSNOR expression under salt stress, implicating that S-nitrosylation might be involved in NO-alleviating salt stress. To further explore whether S-nitrosylation is a key molecular mechanism of NO-alleviating salt stress, the biotin-switch technique and liquid chromatography/mass spectrometry/mass spectrometry (LC-MS/MS) were conducted. A total of 1054 putative S-nitrosylated proteins have been identified, which were mainly enriched in chloroplast, cytoplasm and mitochondrion. Among them, 15 and 22 S-nitrosylated proteins were involved in mitogen-activated protein kinase (MAPK) signal transduction and carbohydrate metabolism, respectively. In MAPK signaling, various S-nitrosylated proteins, SAM1, SAM3, SAM, PP2C and SnRK, were down-regulated and MAPK, MAPKK and MAPKK5 were up-regulated at the transcriptional level by GSNO treatment under salt stress compared to NaCl treatment alone. The GSNO pretreatment could reduce ethylene production and ABA content under NaCl stress. In addition, the activities of enzyme identified in carbohydrate metabolism, their expression at the transcriptional level and the metabolite content were up-regulated by GSNO supplication under salt stress, resulting in the activation of glycolysis and tricarboxylic acid cycle (TCA) cycles. Thus, these results demonstrated that NO might beneficially regulate MAPK signaling at transcriptional levels and activate carbohydrate metabolism at the post-translational and transcriptional level, protecting seedlings from energy deficiency and salinity, thereby alleviating salt stress-induced damage in tomato seedlings. It provides initial insights into the regulatory mechanisms of NO in response to salt stress.

Effects of Kiwifruit Rootstocks with Opposite Tolerance on Physiological Responses of Grafting Combinations under Waterlogging Stress

Kiwifruit is commonly sensitive to waterlogging stress, and grafting onto a waterlogging-tolerant rootstock is an efficient strategy for enhancing the waterlogging tolerance of kiwifruit plants. KR5 (Actinidia valvata) is more tolerant to waterlogging than ‘Hayward’ (A. deliciosa) and is a potential resistant rootstock for kiwifruit production. Here, we focused on evaluating the performance of the waterlogging-sensitive kiwifruit scion cultivar ‘Zhongmi 2′ when grafted onto KR5 (referred to as ZM2/KR5) and Hayward (referred to as ZM2/HWD) rootstocks, respectively, under waterlogging stress. The results showed ‘Zhongmi 2′ performed much better when grafted onto KR5 than when grafted onto ‘Hayward’, exhibiting higher photosynthetic efficiency and reduced reactive oxygen species (ROS) damage. Furthermore, the roots of ZM2/KR5 plants showed greater root activity and energy supply, lower ROS damage, and more stable osmotic adjustment ability than the roots of ZM2/HWD plants under waterlogging stress. In addition, we detected the expression of six key genes involved in the kiwifruit waterlogging response mechanism, and these genes were remarkably induced in the ZM2/KR5 roots but not in the ZM2/HWD roots under waterlogging stress. Moreover, principal component analysis (PCA) further demonstrated the differences in the physiological responses of the ZM2/KR5 and ZM2/HWD plants under waterlogging stress. These results demonstrated that the KR5 rootstock can improve the waterlogging tolerance of grafted kiwi plants by regulating physiological and biochemical metabolism and molecular responses.

Plant photosynthetic overcompensation under nocturnal warming: lack of evidence in subtropical evergreen trees

BACKGROUND AND AIMS

Increased plant photosynthesis under nocturnal warming is a negative feedback mechanism to overcompensate for night-time carbon loss to mitigate climate warming. This photosynthetic overcompensation effect has been observed in dry deciduous ecosystems but whether it exists in subtropical wet forest trees is unclear.

METHODS

Two subtropical evergreen tree species (Schima superba and Castanopsis sclerophylla) were grown in a greenhouse and exposed to ambient and elevated night-time temperature. The occurrence of the photosynthetic overcompensation effect was determined by measuring daytime and night-time leaf gas exchange and non-structural carbohydrate (NSC) concentration.

KEY RESULTS

A reduction in leaf photosynthesis for both species and an absence of persistent photosynthetic overcompensation were observed. The photosynthetic overcompensation effect was transient in S. superba due to respiratory acclimation and stomatal limitation. For S. superba, nocturnal warming resulted in insufficient changes in night-time respiration and NSC concentration to stimulate overcompensation and inhibited leaf stomatal conductance by increasing the leaf-to-air vapour pressure deficit.

CONCLUSIONS

The results indicate that leaf stomatal conductance is important for the photosynthetic overcompensation effect in different tree species. The photosynthetic overcompensation effect under nocturnal warming may be a transient occurrence rather than a persistent mechanism in subtropical forest ecosystems.

Inorganic nitrogen uptake rate of Picea asperata curtailed by fine root acclimation to water and nitrogen supply and further by ectomycorrhizae

Ectomycorrhizal (ECM) fungi colonization and function depend on soil water and nutrient supply. To study the effects of resource supply on ECM colonization and inorganic nitrogen (N) uptake by roots of Picea asperata seedlings, we conducted a study at the end of a 5-year long experiment consisting of five watering regimes (40, 50, 60, 80, and 100% of field capacity) and three NH₄ NO₃ application rates (0 [N0], 20 [N1], and 40 [N2] g N m^-2  year^-1 ). We measured fluxes of ammonium ( NH 4 + ) and nitrate ( NO 3 - ) into colonized and uncolonized roots using noninvasive microtest technology. We found that, across the N supply levels, ECM colonization rate increased by 53 ± 14% from the highest to the lowest level of water supply. Across the watering regimes, the fraction of mycorrhizal root tips was 39 ± 4% higher under native N supply compared to roots grown under N additions. As expected for conifers, both colonized and uncolonized roots absorbed NH 4 + at a higher rate than NO 3 - . N additions reduced the instantaneous ion uptake rates of uncolonized roots grown under low water supply but enhanced the fluxes into roots grown under sufficient soil water availability. Soil water supply improves inorganic N uptake by uncolonized roots but reduces the efficiency of colonized roots. Under the lowest water supply regime, the uptake rate of NH 4 + and NO 3 - by colonized roots was 40-80% of those by uncolonized roots, decreasing to 20-30% as soil water supply improved. Taken together, our results suggest that the role ectomycorrhizae play in the nutrient acquisition of P. asperata seedling likely diminishes with increasing availability of soil resources.

Long-term effects of 7-year warming experiment in the field on leaf hydraulic and economic traits of subtropical tree species

Rising temperature associated with climate change may have substantial impacts on forest tree functions. We conducted a 7-year warming experiment in subtropical China by translocating important native forest tree species (Machilas breviflora, Syzygium rehderianum, Schima superba and Itea chinensis) from cooler high-elevation sites (600 m) to 1-2°C warmer low-elevation sites (300 and 30 m) to investigate warming effects on leaf hydraulic and economic traits. Here, we report data from the last 3 years (Years 5-7) of the experiment. Warming increased leaf hydraulic conductance of S. superba to meet the higher evaporative demand. M. breviflora (300 m), S. rehderianum, S. superba and I. chinensis (300 and 30 m) exhibited higher area-based and mass-based maximum photosynthetic rates (A_a and A_m , respectively) related to increasing stomatal conductance (g_s ) and stomatal density in the wet season, which led to rapid growth; however, we observed decreased growth of M. breviflora at 30 m due to lower stomatal density and decreased A_a in the wet season. Warming increased photosynthetic nitrogen-use efficiency and photosynthetic phosphorus-use efficiency, but reduced leaf dry mass per unit area due to lower leaf thickness, suggesting that these tree species allocated more resources into upregulating photosynthesis rather than into structural investment. Our findings highlight that there was trait variation in the capacity of trees to acclimate to warmer temperatures such that I. chinensis may benefit from warming, but S. superba may be negatively influenced by warming in future climates.

Spatial Distribution of Biomaterial Microenvironment pH and Its Modulatory Effect on Osteoclasts at the Early Stage of Bone Defect Regeneration

It is generally accepted that biodegradable materials greatly influence the nearby microenvironment where cells reside; however, the range of interfacial properties has seldom been discussed due to technical bottlenecks. This study aims to depict biomaterial microenvironment boundaries by correlating interfacial H⁺ distribution with surrounding cell behaviors. Using a disuse-related osteoporotic mouse model, we confirmed that the abnormal activated osteoclasts could be suppressed under relatively alkaline conditions. The differentiation and apatite-resorption capability of osteoclasts were "switched off" when cultured in titrated material extracts with pH values higher than 7.8. To generate a localized alkaline microenvironment, a series of borosilicates were fabricated and their interfacial H⁺ distributions were monitored spatiotemporally by employing noninvasive microtest technology. By correlating interfacial H⁺ distribution with osteoclast "switch on/off" behavior, the microenvironment boundary of the tested material was found to be 400 ± 50 μm, which is broader than the generally accepted value, 300 μm. Furthermore, osteoporotic mice implanted with materials with higher interfacial pH values and boarder effective ranges had lower osteoclast activities and a thicker new bone. To conclude, effective proton microenvironment boundaries of degradable biomaterials were depicted and a weak alkaline microenvironment was shown to promote regeneration of osteoporotic bones possibly by suppressing abnormal activated osteoclasts.