Large Plankton Enhance Heterotrophy Under Experimental Warming in a Temperate Coastal Ecosystem

Microbes are key players in oceanic carbon fluxes. Temperate ecosystems are seasonally variable and thus suitable for testing the effect of warming on microbial carbon fluxes at contrasting oceanographic conditions. In four experiments conducted in February, April, August and October 2013 in coastal NE Atlantic waters, we monitored microbial plankton stocks and daily rates of primary production, bacterial heterotrophic production and respiration at in situ temperature and at 2 and 4°C over ambient values during 4-day incubations. Ambient total primary production (TPP) exceeded total community respiration (< 200 µm, TR) in winter and fall but not in spring and summer. The bacterial contribution to ecosystem carbon fluxes was low, with bacterial production representing on average 6.9 ± 3.2% of TPP and bacterial respiration (between 0.8 and 0.2 µm) contributing on average 35 ± 7% to TR. Warming did not result in a uniform increase in the variables considered, and most significant effects were found only for the 4°C increase. In the summer and fall experiments, under warm and nutrient-deficient conditions, the net TPP/TR ratio decreased by 39 and 34% in the 4°C treatment, mainly due to the increase in respiration of large organisms rather than bacteria. Our results indicate that the interaction of temperature and substrate availability in determining microbial carbon fluxes has a strong seasonal component in temperate planktonic ecosystems, with temperature having a more pronounced effect and generating a shift toward net heterotrophy under more oligotrophic conditions as found in summer and early fall.     

Importance of Seasonality for the Response of a Mesic Temperate Grassland to Increased Precipitation Variability and Warming

Timing of precipitation events within the growing season and the non-uniformity of warming might be decisive for alterations in productivity and community composition, with consequences for ecosystem functioning. The responses of aboveground production, community composition, functional group and species evenness to altered intra-annual precipitation variability and their interactions with winter or summer warming were examined in European, mesic temperate grassland. Increased precipitation variability with an induced spring drought resulted in a 17% reduction in ANPP, and late drought reduced ANPP by 18% compared to regular rainfall patterns throughout the entire growing season. Winter warming increased ANPP by 12%, whereas summer warming showed no significant effect on biomass but decreased species richness. The effects of increased precipitation variability and warming on ANPP were independent of each other. Forbs benefited from high precipitation variability with spring drought events, likely due to reduced competitive pressure by decreasing, water stressed grasses. Increased precipitation variability coinciding with higher summer temperatures led to reduced species evenness and likely promoted the establishment of specialists and drought-tolerant species. Seasonality of climatic factors, here early versus late drought events in the high precipitation variability treatments, was important in driving shifts in community composition but not for decreases in ANPP. Non-uniform warming, here winter versus summer, affected the direction of response of both community composition and ANPP. Variability of resources is affecting ecosystem processes and species interactions. Recognition of seasonality and non-uniformity of climatic factors will improve predictions of plant performance and biotic interactions in response to climate change.     

Seasonal Dynamics of Arbuscular Mycorrhizal Fungal Communities in Roots in a Seminatural Grassland

Symbiotic arbuscular mycorrhizal fungi (AMF) have been shown to influence both the diversity and productivity of grassland plant communities. These effects have been postulated to depend on the differential effects of individual mycorrhizal taxa on different plant species; however, so far there are few detailed studies of the dynamics of AMF colonization of different plant species. In this study, we characterized the communities of AMF colonizing the roots of two plant species, Prunella vulgaris and Antennaria dioica, in a Swedish seminatural grassland at different times of the year. The AMF small subunit rRNA genes were subjected to PCR, cloning, sequencing, and phylogenetic analysis. Nineteen discrete sequence types belonging to Glomus groups A and B and to the genus Acaulospora were distinguished. No significant seasonal changes in the species compositions of the AMF communities as a whole were observed. However, the two plant species hosted significantly different AMF communities. P. vulgaris hosted a rich AMF community throughout the entire growing season. The presence of AMF in A. dioica decreased dramatically in autumn, while an increased presence of Ascomycetes species was detected.     

Warming and Nitrogen Addition Increase Litter Decomposition in a Temperate Meadow Ecosystem

Background

Litter decomposition greatly influences soil structure, nutrient content and carbon sequestration, but how litter decomposition is affected by climate change is still not well understood.

Methodology/Principal Findings

A field experiment with increased temperature and nitrogen (N) addition was established in April 2007 to examine the effects of experimental warming, N addition and their interaction on litter decomposition in a temperate meadow steppe in northeastern China. Warming, N addition and warming plus N addition reduced the residual mass of L. chinensis litter by 3.78%, 7.51% and 4.53%, respectively, in 2008 and 2009, and by 4.73%, 24.08% and 16.1%, respectively, in 2010. Warming, N addition and warming plus N addition had no effect on the decomposition of P. communis litter in 2008 or 2009, but reduced the residual litter mass by 5.58%, 15.53% and 5.17%, respectively, in 2010. Warming and N addition reduced the cellulose percentage of L. chinensis and P. communis, specifically in 2010. The lignin percentage of L. chinensis and P. communis was reduced by warming but increased by N addition. The C, N and P contents of L. chinensis and P. communis litter increased with time. Warming and N addition reduced the C content and C:N ratios of L. chinensisand P. communis litter, but increased the N and P contents. Significant interactive effects of warming and N addition on litter decomposition were observed (P<0.01).

Conclusion/Significance

The litter decomposition rate was highly correlated with soil temperature, soil water content and litter quality. Warming and N addition significantly impacted the litter decomposition rate in the Songnen meadow ecosystem, and the effects of warming and N addition on litter decomposition were also influenced by the quality of litter. These results highlight how climate change could alter grassland ecosystem carbon, nitrogen and phosphorus contents in soil by influencing litter decomposition.     

Sensitivity of Temperate Desert Steppe Carbon Exchange to Seasonal Droughts and Precipitation Variations in Inner Mongolia,China

Arid grassland ecosystems have significant interannual variation in carbon exchange; however, it is unclear how environmental factors influence carbon exchange in different hydrological years. In this study, the eddy covariance technique was used to investigate the seasonal and interannual variability of CO₂ flux over a temperate desert steppe in Inner Mongolia, China from 2008 to 2010. The amounts and times of precipitation varied significantly throughout the study period. The precipitation in 2009 (186.4 mm) was close to the long-term average (183.9±47.6 mm), while the precipitation in 2008 (136.3 mm) and 2010 (141.3 mm) was approximately a quarter below the long-term average. The temperate desert steppe showed carbon neutrality for atmospheric CO₂ throughout the study period, with a net ecosystem carbon dioxide exchange (NEE) of −7.2, −22.9, and 26.0 g C m⁻² yr⁻¹ in 2008, 2009, and 2010, not significantly different from zero. The ecosystem gained more carbon in 2009 compared to other two relatively dry years, while there was significant difference in carbon uptake between 2008 and 2010, although both years recorded similar annual precipitation. The results suggest that summer precipitation is a key factor determining annual NEE. The apparent quantum yield and saturation value of NEE (NEE_sat) and the temperature sensitivity coefficient of ecosystem respiration (R_eco) exhibited significant variations. The values of NEE_sat were −2.6, −2.9, and −1.4 µmol CO₂ m⁻² s⁻¹ in 2008, 2009, and 2010, respectively. Drought suppressed both the gross primary production (GPP) and R_eco, and the drought sensitivity of GPP was greater than that of R_eco. The soil water content sensitivity of GPP was high during the dry year of 2008 with limited soil moisture availability. Our results suggest the carbon balance of this temperate desert steppe was not only sensitive to total annual precipitation, but also to its seasonal distribution.     

Warming and Nitrogen Addition Alter Photosynthetic Pigments,Sugars and Nutrients in a Temperate Meadow Ecosystem

Global warming and nitrogen (N) deposition have an important influence on terrestrial ecosystems; however, the influence of warming and N deposition on plant photosynthetic products and nutrient cycling in plants is not well understood. We examined the effects of 3 years of warming and N addition on the plant photosynthetic products, foliar chemistry and stoichiometric ratios of two dominant species, i.e., Leymus chinensis and Phragmites communis, in a temperate meadow in northeastern China. Warming significantly increased the chlorophyll content and soluble sugars in L. chinensis but had no impact on the carotenoid and fructose contents. N addition caused a significant increase in the carotenoid and fructose contents. Warming and N addition had little impact on the photosynthetic products of P. communis. Warming caused significant decreases in the N and phosphorus (P) concentrations and significantly increased the carbon (C):P and N:P ratios of L. chinensis, but not the C concentration or the C:N ratio. N addition significantly increased the N concentration, C:P and N:P ratios, but significantly reduced the C:N ratio of L. chinensis. Warming significantly increased P. communis C and P concentrations, and the C:N and C:P ratios, whereas N addition increased the C, N and P concentrations but had no impact on the stoichiometric variables. This study suggests that both warming and N addition have direct impacts on plant photosynthates and elemental stoichiometry, which may play a vital role in plant-mediated biogeochemical cycling in temperate meadow ecosystems.     

Risk Assessment for Key Socio-Economic and Ecological Species in a Sub-Arctic Marine Ecosystem Under Combined Ocean Acidification and Warming

Ecosystems - The Arctic may be particularly vulnerable to the consequences of both ocean acidification (OA) and global warming, given the faster pace of these processes in comparison with global...     

Relationship of Productivity to Species Richness in the Xinjiang Temperate Grassland

The relationship between species richness (SR) and aboveground net primary productivity (ANPP) is still a central and debated issue in community ecology. Previous studies have often emphasized the relationship of alpha diversity (number of species identity) to the mean ANPP with respect to the SR-ANPP relationship while neglecting the contribution of beta diversity (dissimilarity in species composition) to the mean ANPP and to the stability of ANPP (coefficient of ANPP: CV of ANPP). In this study, we used alpha and beta diversity, mean ANPP and the CV of ANPP collected from 159 sites and belonging to three vegetation types in the Xinjiang temperate grassland to first examine their trends along climatic factors and among different vegetation types and then test the relationship among alpha (beta) diversity and mean ANPP and the CV of ANPP. Our results showed that in the Xinjiang temperate grasslands, alpha diversity was positively and linearly correlated with MAP but unimodally correlated with MAT. Meanwhile, beta diversity was unimodally correlated with MAP but linearly correlated with MAT. Relative to desert steppe, meadow steppe and typical steppe had the highest alpha and beta diversity, respectively. Except for ANPP exhibiting a quadratic relationship with MAP, no significant relationship was found among ANPP, the CV of ANPP and climatic factors. ANPP and the CV of ANPP also exhibited no apparent patterns in variation among different vegetation types. Our results further showed that mean ANPP was closely associated with alpha diversity. Both linear and unimodal relationships were detected between alpha diversity and mean ANPP, but their particular form was texture-dependent. Meanwhile, the CV of ANPP was positively correlated with beta diversity. Our results indicated that in addition to incorporating alpha diversity and mean ANPP, incorporating beta diversity and the CV of ANPP could expand our understanding of the SR-ANPP relationship.     

Responses of Plant Community Composition and Biomass Production to Warming and Nitrogen Deposition in a Temperate Meadow Ecosystem

Climate change has profound influences on plant community composition and ecosystem functions. However, its effects on plant community composition and biomass production are not well understood. A four-year field experiment was conducted to examine the effects of warming, nitrogen (N) addition, and their interactions on plant community composition and biomass production in a temperate meadow ecosystem in northeast China. Experimental warming had no significant effect on plant species richness, evenness, and diversity, while N addition highly reduced the species richness and diversity. Warming tended to reduce the importance value of graminoid species but increased the value of forbs, while N addition had the opposite effect. Warming tended to increase the belowground biomass, but had an opposite tendency to decrease the aboveground biomass. The influences of warming on aboveground production were dependent upon precipitation. Experimental warming had little effect on aboveground biomass in the years with higher precipitation, but significantly suppressed aboveground biomass in dry years. Our results suggest that warming had indirect effects on plant production via its effect on the water availability. Nitrogen addition significantly increased above- and below-ground production, suggesting that N is one of the most important limiting factors determining plant productivity in the studied meadow steppe. Significant interactive effects of warming plus N addition on belowground biomass were also detected. Our observations revealed that environmental changes (warming and N deposition) play significant roles in regulating plant community composition and biomass production in temperate meadow steppe ecosystem in northeast China.     

Root Biomass Dynamics Under Experimental Warming and Doubled Precipitation in a Tallgrass Prairie

Human-induced climate change is expected to increase both the frequency and severity of extreme climate events, but their ecological impacts on root dynamics are poorly understood. We conducted a 1-year pulse warming and precipitation experiment in a tallgrass prairie in Oklahoma, USA to examine responses of root dynamics. We collected data in the pre-treatment year of 2002, imposed four treatments (control, 4°C warming, doubled precipitation, and warming plus doubled precipitation) in 2003, and observed post-treatment effects in 2004. Root biomass dynamics (for example, root growth and death) were measured using sequential coring and ingrowth coring methods. Treatment effects were not significant on standing root biomass in 2003, although root growth rate was significantly higher in the warmed than control plots. However, in the post-treatment year, the warmed plots had significantly lower standing root biomass than the controls, likely resulting from increased root death rate. Root death rate was significantly lower in the doubled precipitation and warmed plus doubled precipitation plots than that in the warmed plots in 2004. The root:shoot ratio showed similar responses to the post-treatments as standing root biomass, whereas aboveground biomass changed relatively little, indicating that roots were more sensitive to lagged effects than aboveground biomass. Our results demonstrate that root growth and death rates are highly sensitive to extreme climate events and lagged effects of extreme climate on root dynamics are important in assessing terrestrial carbon-cycle feedbacks to climate change.     

The Role of Photodegradation in Surface Litter Decomposition Across a Grassland Ecosystem Precipitation Gradient

Differences in litter decomposition patterns among mesic, semiarid, and arid grassland ecosystems cannot be accurately explained by variation in temperature, moisture, and litter chemistry alone. We hypothesized that ultraviolet (UV) radiation enhances decomposition in grassland ecosystems via photodegradation, more so in arid compared to mesic ecosystems, and in litter that is more recalcitrant to microbial decomposition (with high compared to low lignin concentrations). In a 2-year field study, we manipulated the amount of UV radiation reaching the litter layer at three grassland sites in Minnesota, Colorado, and New Mexico, USA, that represented mesic, semiarid, and arid grassland ecosystems, respectively. Two common grass leaf litter types of contrasting lignin:N were placed at each site under screens that either passed all solar radiation wavelengths or passed all but UV wavelengths. Decomposition was generally faster when litter was exposed to UV radiation across all three sites. In contrast to our hypothesis, the contribution of photodegradation in the decomposition process was not consistently greater at the more arid sites or for litter with higher lignin content. Additionally, at the most arid site, exposure to UV radiation could not explain decomposition rates that were faster than expected given climate constraints or lack of N immobilization by decomposing litter. Although photodegradation plays an important role in the decomposition process in a wider range of grassland sites than previously documented, it does not fully explain the differences in decomposition rates among grassland ecosystems of contrasting aridity.     

Bryophyte Mats Inhibit Germination of Non-native Species in Burnt Temperate Native Grassland Remnants

Species-rich native grasslands in western Victoria, Australia, are often small, have a high perimeter to area ratio and are surrounded by non-native species. Few non-native species, however, have invaded them. A feature of species-rich grasslands is the presence of a bryophyte mat (composed of mosses and liverworts) that carpets the intertussock spaces. I assessed the role of these mats in plant invasions by sowing three non-native species (Briza maxima, Hypochoeris radicata, Plantago lanceolata) in replicated disturbed (mats removed) and undisturbed (mats intact) microsites at three grassland remnants (two recently burnt, one unburnt for 3 years) and followed seedling emergence, survival and growth for 5 months. Three native species were also sown for comparison. The rate of germination and total percent germination of non-native species were significantly enhanced at both burnt sites when the mat was disturbed. The large-seeded Briza maxima failed to germinate at both burnt sites in the absence of soil disturbance. The native species generally did not show a strong germination or growth response to soil disturbance in burnt areas. At the unburnt site, where monthly percent soil moisture was highest, final percent germination of the non-native and native species was greatest of any site in both microsites, and germination was not significantly affected by soil disturbance. Differences in the seed morphology of native and non-native species may play an important role in their ability to establish on bryophyte mats in moisture-limiting environments. Any activity that disrupts the mats in the frequently burnt, species-rich grassland remnants is likely to significantly enhance the germination and subsequent growth by non-natives. However, where burning is infrequent, germination of some non-native species may be expected, regardless of disturbance, although growth will likely be favoured in disturbed areas.     

Controls over Soil Nitrogen Pools in a Semiarid Grassland Under Elevated CO2 and Warming

Long-term responses of terrestrial ecosystems to the combined effects of warming and elevated CO₂ (eCO₂) will likely be regulated by N availability. The stock of soil N determines availability for organisms, but also influences loss to the atmosphere or groundwater. eCO₂ and warming can elicit changes in soil N via direct effects on microbial and plant activity, or indirectly, via soil moisture. Detangling the interplay of direct- and moisture-mediated impacts on soil N and the role of organisms in controlling soil N will improve predictions of ecosystem-level responses. We followed individual soil N pools over two growing seasons in a semiarid temperate grassland, at the Prairie Heating and CO₂ Enrichment experiment. We evaluated relationships of N pools with environmental factors and explored the role of plants by assessing plant biomass, plant N, and plant inputs to soil. We also assessed N forms in plots with and without vegetation to remove plant-mediated effects. Our study demonstrated that the effects of warming and eCO₂ are highly dependent on individual N form and on year. In this water-constrained grassland, eCO₂, warming and their combination appear to impact soil N pools through a complex combination of direct- and moisture-mediated effects. eCO₂ decreased NO₃ ^? but had neutral to positive effects on NH₄ ⁺ and dissolved organic N (DON), particularly in a wet year. Warming increased NO₃ ^? availability due to a combination of indirect drying and direct temperature-driven effects. Warming also increased DON only in vegetated plots, suggesting plant mediation. Our results suggest that impacts of combined eCO₂ and warming are not always equivalent for plant and soil pools; although warming can help offset the decrease in NO₃ ^? availability for plants under eCO₂, the NO₃ ^? pool in soil is mainly driven by the negative effects of eCO₂.     

Evaluation of Some Phenological and Biochemical Characteristics of Selected New Late Flowering Dried Apricot Cultivars

In this study, promising candidates of six apricot genotypes were compared with our local and major cultivar (Hac?halilo?lu) based on their phenological, pomological, and biochemical characteristics. Fruit weight, stone weight, flesh firmness, flesh fruit/stone ratio, TSS (Total soluble solids), glucose, fructose, sucrose, total phenols, total antioxidant activity (FRAP and ABTS assays) and bud break, first bloom, full bloom, and harvesting date of apricot cultivar candidates were compared with cultivar Hac?halilo?lu ‘HH.’ According to the obtained results, the higher content of total phenolic compounds and total antioxidant activity was determined in the N95 genotype (96.87 µmol TE/g) fruit, whereas the ‘HH’ cultivar was characterized by the lower value (94.6 µmol TE/g) especially determined by FRAP method. Individual sugars and the soluble solids content of fruit differed between selected genotypes and ‘HH’ cultivar. Glucose, fructose, and sucrose contents were higher in all selected genotypes than in Hac?halilo?lu cultivar.     

Photosynthetic and Respiratory Acclimation to Experimental Warming for Four Species in a Tallgrass Prairie Ecosystem

Global temperature has been Increased by 0.6 ℃ over the past century and is predicted to Increase by 1.4-5.8 ℃ by the end of this century. It is unclear what impacts global warming will have on tallgrass species. In the present study, we examined leaf net photosynthetic rate （P.） and leaf respiration rate in darkness （Rd） of Aster erlcoldes （L.） Nesom, Ambrosia psllostachya DC., Helianthus mollis Lam., and Sorghastrum nutans （L.） Nash In response to experimental warming in a tallgrass prairie ecosystem of the Great Plains, USA, in the autumn （fall） of 2000 and through 2001. Warming has been Implemented with infrared heaters since 21 November 1999. The P. increased significantly In spring, decreased in early fall, and did not change in summer and late fall in the four species under warming compared with control. The Rd of the four species increased significantly until mid-summer and then did not change under warming. Measured temperature-response curves of P. showed that warming Increased the optimum temperature of P. （Topt） by 2.32 and 4.59 ℃ for H. mollis and S. nutans, respectively, in August, whereas there were no changes in May and September, and A. ericoldes and A. psllostachya also showed no changes in any of the 3 months. However, P. at optimum temperature （Popt） showed downregulation in September and no regulation in May and August for all four species. The temperature-response curves of Rd Illustrate that the temperature sensitivity of Rd, Q10, was lower in the warmed plots compared with the control plots, except for A. ericoides in August, whereas there were no changes In May and September for all four species. The results of the present study indicate that photosynthetic and respiratory acclimation varies with species and among seasons, occurring In the mid-growing season and not in the early and late growing seasons.     

Nutrient and Sediment Retention in a Temperate Marsh Ecosystem

The Wye marsh, an undeveloped wetland of 639.9 ha, serves as a receiving water for a 19,600 ha agricultural watershed before discharging into the Great Lakes. Seasonal and diel changes in limnological variables, most notably nitrogen, phosphorus, silica and turbidity, have been examined in the Wye river, marsh and discharge waters over an 11-month period and related to the composition of marsh sediments. Retention rates of the marsh ecosystem for incoming nutrients and suspended solids have been estimated by calculations of mean monthly inflow to outflow ratios using the levels of these factors in the Wye River and the marsh discharge. Calculated mean monthly retention rates of the marsh for incoming nutrients is estimated at no less than 61% for nitrogen-N, 36% for total phosphate, and 14% for soluble silica during the ice-free period. Based on observed turbidity levels, the retention of incoming suspended solids is estimated at 65% for the same period. The Wye marsh is a substantial sump for inorganic and organic materials which are retained within the water column, biomass and unconsolidated sediments.     

The Seasonal Pattern of Growth and Production of a Temperate C4 Species, Cyperus longus

Growth and production of the temperate C₄ species Cyperus longusL. was measured throughout a growing season in an establishedplot in Eastern Ireland. The maximum standing live biomass reachedwas 2·5 kg m^–2. Estimates of unit leaf rate (ULR)and leaf area index (LAI) were made. The product of these quantitiesgave the crop growth rate (CGR) each week. C. longus was foundto maintain high values of LAI throughout the summer, with amaximum value of about 13 in early August. CGR reached a peakin early July. The optimum LAI was 11·6. Temperaturesat five levels in the plant canopy, and the amount of solarradiation intercepted by the canopy were measured continuouslyduring the summer. The mean daily rate of leaf extension waspositively correlated with the mean daily air temperature abovethe canopy but the temperature coefficient of the process waslow compared with other temperate species. The percentage ofsolar radiation intercepted by the canopy increased rapidlyin early summer, and canopy closure had occurred by mid-June.Rates of net photosynthesis were measured on young and old leafmaterial in situ at the time of peak LAI. In young leaves themaximum rates of net photosynthesis were higher than those publishedfor a range of temperate C₃ species, but similar to those foundin another temperate C₄ species, Spartina townsendii. Key words: C₄ photosynthesis, leaf growth, productivity     

Effects of Warming, Summer Drought, and CO2 Enrichment on Aboveground Biomass Production, Flowering Phenology, and Community Structure in an Upland Grassland Ecosystem

Future climate scenarios predict simultaneous changes in environmental conditions, but the impacts of multiple climate change drivers on ecosystem structure and function remain unclear. We used a novel experimental approach to examine the responses of an upland grassland ecosystem to the 2080 climate scenario predicted for the study area (3.5°C temperature increase, 20% reduction in summer precipitation, atmospheric CO₂ levels of 600 ppm) over three growing seasons. We also assessed whether patterns of grassland response to a combination of climate change treatments could be forecast by ecosystem responses to single climate change drivers. Effects of climate change on aboveground production showed considerable seasonal and interannual variation; April biomass increased in response to both warming and the simultaneous application of warming, summer drought, and CO₂ enrichment, whereas October biomass responses were either non-significant or negative depending on the year. Negative impacts of summer drought on production were only observed in combination with a below-average rainfall regime, and showed lagged effects on spring biomass. Elevated CO₂ had no significant effect on aboveground biomass during this study. Both warming and the 2080 climate change scenario were associated with a significant advance in flowering time for the dominant grass species studied. However, flowering phenology showed no significant response to either summer drought or elevated CO₂. Species diversity and equitability showed no response to climate change treatments throughout this study. Overall, our data suggest that single-factor warming experiments may provide valuable information for projections of future ecosystem changes in cool temperate grasslands.     

The Influence of Altered Rainfall Regimes on Early Season N Partitioning Among Early Phenology Annual Plants,a Late Phenology Shrub,and Microbes in a Semi-arid Ecosystem

In Mediterranean-type ecosystems, nitrogen (N) accumulates in soil during dry summer months and rapidly becomes available during early season rain events. The availability of early season N could depend on the size of rainfall events, soil microbial activity, and phenology of the plant community. However, it is poorly understood how precipitation patterns affect the fate of early season N. Microbes and plants with early phenology may compete strongly for early season N but theory suggests that microbial N storage can meet plant N demands later in the season. Using a ¹⁵N tracer and rainfall manipulation we investigated the fate of early season N. N allocation patterns differed substantially between microbes, early and late phenology plants. As expected early phenology annuals and microbes took up ¹⁵N, within 1 day, whereas a late-phenology shrub allocated ¹⁵N to leaves later in the season. We saw no evidence for microbial storage of early season N; the peak of ¹⁵N in shrub leaves did not coincide with detectable levels of ¹⁵N in the microbial biomass or labile soil pool. This suggests that shrubs were able to access early season N, store and allocate it for growth later in the season. Although we saw no evidence of microbial N storage, N retention in soil organic matter (SOM) was high and microbes may play an important role in sequestering N to SOM. Plant N uptake did not respond significantly to 1 year of rainfall manipulation, but microbes were sensitive to dry conditions. 1 year after ¹⁵N addition shrubs had resorbed up to half of the N from leaves whereas N in annuals remained as dead leaf litter. Differences in end-of-season N partitioning between dead and living biomass in the two vegetation types suggest that plant species composition could affect N availability in the following growing season, but it may take several years of altered precipitation patterns to produce rainfall-dependent changes.