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Terrestrial ecosystems worldwide are receiving increasing amounts of biologically reactive nitrogen (N) as a consequence of anthropogenic activities. This intended or unintended fertilization can have a wide‐range of impacts on biotic communities and hence on soil respiration. Reduction in below‐ground carbon (C) allocation induced by high N availability has been assumed to be a major mechanism determining the effects of N enrichment on soil respiration. In addition to increasing available N, however, N enrichment causes soil acidification, which may also affect root and microbial activities. The relative importance of increased N availability vs. soil acidification on soil respiration in natural ecosystems experiencing N enrichment is unclear. We conducted a 12‐year N enrichment experiment and a 4‐year complementary acid addition experiment in a semi‐arid Inner Mongolian grassland. We found that N enrichment had contrasting effects on root and microbial respiration. N enrichment significantly increased root biomass, root N content and specific root respiration, thereby promoting root respiration. In contrast, N enrichment significantly suppressed microbial respiration likely by reducing total microbial biomass and changing the microbial community composition. The effect on root activities was due to both soil acidity and increased available N, while the effect on microbes primarily stemmed from soil acidity, which was further confirmed by results from the acid addition experiment. Our results indicate that soil acidification exerts a greater control than soil N availability on soil respiration in grasslands experiencing long‐term N enrichment. These findings suggest that N‐induced soil acidification should be included in predicting terrestrial ecosystem C balance under future N deposition scenarios.

Aims Specific root respiration (RR S ) is a key root trait, determining i.e. nutrient foraging and uptake efficiencies. However, a considerable uncertainty exists regarding the effects of storage time and conditions on RR S measurements. Methods Fine root CO 2 efflux rates of three plant types (tree seedling Carpinus betulus , legume Pisum sativum , grass Lolium perenne ) were measured as depending on storage time (30–1440 min post-rinsing) and conditions (i.e. attached to plant, warm and cold water storage, and storage under dry conditions). Results Short-term storage conditions (30 min) had a significant effect on measured RR S rates, in specific, RR S rates of all three species were significantly lower under dry storage. Irrespective of plant species or temperature, storage of excised roots in water did not affect RR S for 300 min,. RR S measurements remained stable for 1 day if roots were stored cold. Conclusions Our results have important implications on measurement routines of RR S —a generally understudied root trait. Henceforth it seems reasonable to collect roots in the field and transport them, hydrated but even uncooled, to the laboratory for subsequent measurements for at least 300 min post-rinsing.

The response of belowground biological processes to soil N availability in Larix gmelinii (larch) and Fraxinus mandshurica (ash) plantations was studied. Soil and root respiration were measured with Li-Cor 6400 and gas-phase O₂ electrodes, respectively. Compared with the control, N fertilization induced the decreases of fine root biomass by 52% and 25%, and soil respiration by 30% and 24% in larch and ash plantations, respectively. The average soil microbial biomass C and N were decreased by 29% and 42% under larch stand and 39% and 47% under ash stand, respectively. While the fine root tissue N concentration under fertilized plots was higher 26% and 12% than that under control plots, respectively, the average fine root respiration rates were increased by 10% and 13% in larch and ash stands under fertilized plot, respectively. Soil respiration rates showed significantly positive exponential relationships with soil temperature, and a seasonal dynamic. These findings suggest that N fertilization can suppress fine root biomass at five branch orders (<2 mm in diameter), soil respiration, and soil microbial biomass C and N, and alter soil microbial communities in L. gmelinii and F. mandshurica plantations.

Fertilization is a common, cost-effective method to increase productivity of managed forests in the southeastern United States; however, little is known about how fertilization will affect the processes that drive total soil CO2 efflux (F S) and ultimately net ecosystem productivity (NEP). The objective of this research was to intensively monitor the response of F S, and its respiratory components during the first year after N and P fertilization in Pinus taeda clones. We monitored F S, heterotrophic respiration (R H), and specific root respiration (R R) and found that F S in fertilized plots differed significantly (P < 0.0001) from that in unfertilized plots, but the direction of this effect was dependent on date. Additionally, R H was consistently lower (P = 0.0001) in fertilized plots relative to control plots, but the magnitude was dependent on the sampling date, and R R significantly (P = 0.04) increased in fertilized plots (+20%) when averaged over the study. Increased R R and decreased R H were probably offsetting each other, resulting in no overall difference in F S 1 year after fertilization. If these short-term trends persisted over the rotation of the stand, increased gross primary productivity accompanied by no change or even a decrease in soil C evolution could result in increased NEP.

Copper (Cu) is a micronutrient essential for plant development. However, in excess, it is toxic to plants and may cause various physiological and morphological changes. The study of the growth of plants exposed to excess Cu is important for the development of phytoremediation programs and for understanding the mechanisms involved in the tolerance of this metal. In this context, the objective of this research was to evaluate the effect of excess copper on photosynthetic responses and root morphology of Hymenaea courbaril L. Biometric measurements, gas exchange, root morphology, and Cu content in tissues and indices (TI and TF) were assessed, involving metal content and biomass. Up to a concentration of 200 mg kg−1, Cu favored growth, gas exchange, and root morphology of the plants under study. At a higher concentration (800 mg kg−1) in the soil, it affected plant growth and caused a decrease in photosynthetic rate. Biochemical limitations in photosynthesis were observed, as well as lower maximum net photosynthetic rate (Amax), respiration rate in the dark (Rd), light compensation point (LCP), light saturation point (LSP), and apparent quantum yield (α), when exposed to excess Cu. Root length, surface area, mean diameter, root volume, dry biomass, and specific root length decreased with high Cu concentrations in the soil. Cu was accumulated in the roots as a mechanism of tolerance to the excess of this metal in order to preserve the most metabolically active tissues present in the leaves. At a concentration of 800 mg kg−1, copper also caused inhibition of the root system. Plants of H. courbaril showed tolerance to excess Cu in the soil and can be indicated for the recovery of areas contaminated with this metal.

AIMS: We examined the physiological and morphological responses of individual fine root segments in boreal forests stands with different age since the last fire to determine changes in specific fine root respiration and morphological traits during forest succession. METHODS: We investigated the respiration of fine roots divided into three diameter classes (<0.5, 0.5–1.0, and 1.0–2.0 mm) in a Finnish boreal Pinus sylvestris L. in forest stands with 5, 45, 63, and 155 years since the last fire. RESULTS: Specific respiration rates of <0.5 mm roots in 155-year-old stands were 74 %, 38 %, and 31 % higher than in 5-, 45-, and 63-year-old stands, respectively. However, the respiration rates of thicker diameter roots did not significantly change among stands with respect to time after fire. Similarly, fire disturbance had a strong impact on morphological traits of <0.5 mm roots, but not on thicker roots. Root respiration rates correlated positively with specific root length (length per unit mass) and negatively with root tissue density (mass per unit volume) in all stand ages. The linear regression lines fitted to the relationships between root respiration and specific root length or root tissue density showed significantly higher intercepts in 63- and 155-year-old than in 5-year-old stands. CONCLUSION: Significant shifts in the intercept of the common slope of respiration vs. morphology indicate the different magnitude of the changes in physiological performance among the fire age class. Despite a specific small geographic area, we suggest that the recovery of boreal forests following wildfire induces a strategy that favors carbon investment in nutrient and water exploitation efficiency with consequences for higher respiration, length, and lower tissue density of very fine roots.

Carbon allocated to roots accounts for a large portion of net primary productivity, but the fate of that carbon is poorly understood. Absorptive fine roots are the primary way in which plants acquire nutrients. Previous studies have evaluated relationships among root morphological traits, including specific root length, root tissue density, and mycorrhizal colonization, across broad functional and taxonomic groups to test for the existence of a root economics spectrum (RES). Fine roots also release carbon dioxide through respiration, and other studies have found relationships between root morphological traits and root respiration within individual tree species. The objective of this study was to measure a suite of root traits in six co‐occurring temperate tree species that represent a diverse set of aboveground traits to determine whether and how root characteristics influenced root respiration both within and among species. At the Harvard Forest in Petersham, Massachusetts, USA, we measured fine root respiration, root morphology, percent colonization for ectomycorrhizal species, and carbon and nitrogen concentrations on 292 roots from six tree species in June and July 2018. We found that most fine root morphological characteristics varied nearly as much within each tree species as they did among the six species. Root traits were dynamic over time during the two months of our study, where the magnitude of weekly mean trait values varied 32–95% across the study period. Strong correlations among traits suggested trade‐offs on a spectrum from resource acquisition (long, thin, high‐nitrogen roots) to resource conservation (thick, dense, low‐nitrogen roots), and traits were not clustered by tree species within this spectrum. Along with temperature and weekly temporal variation, the resource acquisition strategy (long and thin roots that were high in nitrogen) was associated with higher root respiration, and this relationship was consistent among the six species. This study supported a strong link between the RES and respiration independent of species identity, which provides insight into functional axes for scaling root respiration from individual trees to the forest stand to better quantify belowground carbon flux.

Aims Respiration of sugar maple ( Acer saccharum ) surface fine roots has been shown to partially acclimate to experimentally increased soil temperature. In this study, we assessed how larger roots and roots at deeper depths responded to experimental warming. Methods We quantified specific root respiration and root biomass for three different diameter classes (<1, 1–2, and 2–10 mm) from three soil depths (0–10, 10–30, and 30–50 cm) in a sugar maple forest that had received a factorial combination of increased soil temperature (4 to 5 °C above ambient) and supplemental precipitation for three growing seasons. Results Partial temperature acclimation occurred for respiration of fine-roots (<1 mm) at 0–10 cm, limiting the increase to 30% above that for roots in the control treatment. In contrast, there was no evidence for acclimation of fine-roots at deeper depths, where soil warming caused respiration to more than double. There was evidence of acclimation for 1–2 mm roots at the 0–10 cm depth (20% reduction in respiration at an 18 °C reference temperature) but not for the larger diameter roots at any of the three soil depths. Root biomass was not altered by soil warming or moisture addition. Conclusions Despite partial thermal acclimation in surface fine-root respiration, soil warming caused an overall 41% increase in the C flux to the atmosphere from respiration of roots in the upper 30 cm of soil, from 21.3 to 30.1 μmol m −2  s −1 , potentially reducing C availability for biomass production.

$\\bullet$ Here, we tested hypothesized relationships among leaf and fine root traits of grass, forb, legume, and woody plant species of a savannah community. $\\bullet$ CO2 exchange rates, structural traits, chemistry, and longevity were measured in tissues of 39 species grown in long-term monocultures. $\\bullet$ Across species, respiration rates of leaves and fine roots exhibited a common regression relationship with tissue nitrogen (N) concentration, although legumes had lower rates at comparable N concentrations. Respiration rates and N concentration declined with increasing longevity of leaves and roots. Species rankings of leaf and fine-root N and longevity were correlated, but not specific leaf area and specific root length. The C3 and C4 grasses had lower N concentrations than forbs and legumes, but higher photosynthesis rates across a similar range of leaf N. $\\bullet$ Despite contrasting photosynthetic pathways and N2-fixing ability among these species, concordance in above- and below-ground traits was evident in comparable rankings in leaf and root longevity, N and respiration rates, which is evidence of a common leaf and root trait syndrome linking traits to effects on plant and ecosystem processes.

Leaf area growth determines the light interception capacity of a crop and is often used as a surrogate for plant growth in high-throughput phenotyping systems. The relationship between leaf area growth and growth in terms of mass will depend on how carbon is partitioned among new leaf area, leaf mass, root mass, reproduction, and respiration. A model of leaf area growth in terms of photosynthetic rate and carbon partitioning to different plant organs was developed and tested with Arabidopsis thaliana L. Heynh. ecotype Columbia (Col-0) and a mutant line, gigantea-2 (gi-2), which develops very large rosettes. Data obtained from growth analysis and gas exchange measurements was used to train a genetic programming algorithm to parameterize and test the above model. The relationship between leaf area and plant biomass was found to be non-linear and variable depending on carbon partitioning. The model output was sensitive to the rate of photosynthesis but more sensitive to the amount of carbon partitioned to growing thicker leaves. The large rosette size of gi-2 relative to that of Col-0 resulted from relatively small differences in partitioning to new leaf area vs. leaf thickness.