Mosses often have positive effects on soil carbon and nitrogen cycling, but we know little about how environmentally determined cycles of desiccation and rehydration in mosses influence these processes. In this context, we compared carbon and nitrogen in throughfall after precipitation passed through eight moss species that were either hydrated continuously or desiccated and rehydrated. Also, the throughfall of four moss species was added to soil and used to determine the net effect of carbon and nitrogen added in moss throughfall on soil CO2 and N2O efflux. Depending on the species, desiccated‐rehydrated (rehydrated) mosses lost 2–31 times more carbon in throughfall than mosses that were continuously hydrated (hydrated). Hydrated mosses lost little to no detectable nitrogen, whereas most rehydrated mosses lost some nitrogen in throughfall. Throughfall from both hydrated and rehydrated mosses generated higher CO2 and N2O efflux than water treated soils, but rehydrated moss throughfall promoted larger N2O efflux than hydrated moss throughfall. Throughfall from hydrated mosses caused net negative changes in soil carbon and had very little effect on soil nitrogen, whereas throughfall from rehydrated mosses generated positive changes in soil carbon and nitrogen. Synthesis. Our results indicate that resources lost from desiccated mosses during rehydration influence soil carbon and nitrogen transformations and may be important drivers of carbon and nitrogen cycling and storage in ecosystems.

1. Exotic plant species commonly exploit disturbances more successfully than native plants. This outcome is widely attributed to the fact that disturbance reduces biotic resistance from native plant competitors. However, biocrusts, communities of mosses, lichens, and micro-organisms, are a prominent component of semi-arid grasslands occurring in the interstitial spaces between vascular plants. Biocrusts may provide an important source of biotic resistance to invaders, different from native plant competition, but poorly understood.2. We established a large-scale field experiment to examine how intact versus disturbed biocrusts influenced the emergence and establishment of four native and four exotic plant species in intermountain bunchgrass systems over 2 years-one wet and one dry. We also conducted a complementary greenhouse experiment to explore how differences in moisture might influence biocrust effects on germination.3. In the greenhouse, biocrusts inhibited the germination of both native and exotic plants in the high moisture treatment only. In field experiments, biocrusts inhibited the overall emergence of exotic seedlings in the wetter of the 2 years and inhibited the establishment of exotic seedlings in both years, but they had no overall effect on the emergence or establishment of native seedlings. We found that intact biocrusts in intermountain grasslands can suppress the establishment of some exotic plants, but have much weaker effects on natives. They also suggest that water availability may influence biocrust effects on seed germination. Synthesis.Our results indicate that intact biocrusts may provide an important source of biotic resistance to exotic plant invasions in intermountain grasslands. Furthermore, precipitation inputs may mediate biocrust effects on plant establishment. K E Y W O R D S

The results demonstrate that the larger morphology and the greater physiological output of female C. purpureus gametophytes compared with males occurs across populations and is likely to have significant effects on resource allocation and biotic interactions. However, this high level of dimorphism does not explain population sex ratio variation in the three study populations tested. This research lays the groundwork for future studies on how differential sex-specific variation in cell and leaf traits influences bryophyte plant fitness.

PREMISE Desiccation tolerance (DT) is a widespread phenomenon among land plants, and variable ecological strategies for DT are likely to exist. Using Syntrichia caninervis, a dryland moss and model system used in DT studies, we hypothesized that DT is lowest in juvenile (protonemal) tissues, highest in asexual reproductive propagules (gemmae), and intermediate in adults (shoots). We tested the long‐standing hypothesis of an inherent constitutive strategy of DT in this species. METHODS Plants were rapidly dried to levels of equilibrating relative humidity (RHeq) ranging from 0 to 93%. Postrehydration recovery was assessed using chlorophyll fluorescence, regeneration rates, and visual tissue damage. For each life phase, we estimated the minimum rate of drying (RoDmin) at RHeq = 42% that did not elicit damage 24 h postrehydration. RESULTS DT strategy varied with life phase, with adult shoots having the lowest RoDmin (10‒25 min), followed by gemmae (3‒10 h) and protonema (14‒20 h). Adult shoots exhibited no detectable damage 24 h postrehydration following a rapid‐dry only at the highest RHeq used (93%), but when dried to lower RHs the response declined to <50% of control fluorescence values. Notably, immediately following rehydration (0 h postrehydration), shoots were damaged below control levels of fluorescence regardless of the RHeq, thus implicating damage. CONCLUSIONS Life phases of the moss S. caninervis had a range of strategies from near constitutive (adult shoots) to demonstrably inducible (protonema). A new response variable for assessing degree of DT is introduced as the minimum rate of drying from which full recovery occurs.