Mechanisms behind species-specific water economy responses to water level drawdown in peat mosses

BACKGROUND AND AIMS

The ecosystem engineers Sphagnum (peat mosses) are responsible for sequestering a large proportion of carbon in northern peatlands. Species may respond differently to hydrological changes, and water level changes may lead to vegetation shifts in peatlands, causing them to revert from sinks to sources of carbon. We aimed to compare species-specific responses to water level drawdown within Sphagnum, and investigate which traits affect water economy in this genus.

METHODS

In a mesocosm experiment, we investigated how water level drawdown affected water content (WC) in the photosynthetically active apex of the moss and maximum quantum yield of photosystem II (i.e. Fv/Fm) of 13 Sphagnum species. Structural traits were measured, and eight anatomical traits were quantified from scanning electron microscopy micrographs.

KEY RESULTS

Mixed-effects models indicated that at high water level, large leaves were the most influential predictor of high WC, and at low water level WC was higher in species growing drier in the field, with larger hyaline cell pore sizes and total pore areas associated with higher WC. Higher stem and peat bulk density increased WC, while capitulum mass per area and numerical shoot density did not. We observed a clear positive relationship between Fv/Fm and WC in wet-growing species.

CONCLUSIONS

While we found that most hummock species had a relatively high water loss resistance, we propose that some species are able to maintain a high WC at drawdown by storing large amounts of water at a high water level. Our result showing that leaf traits are important warrants further research using advanced morphometric methods. As climate change may lead to more frequent droughts and thereby water level drawdowns in peatlands, a mechanistic understanding of species-specific traits and responses is crucial for predicting future changes in these systems.

Hyaline cell-rich chondroid syringoma of the finger

A mixed tumor is a neoplasm that has microscopic features of both epithelial and mesenchymal differentiation. Such mixed tumors are known as pleomorphic adenomas in the salivary glands, and their cutaneous counterparts are called chondroid syringomas. These tumors commonly occur in the head and neck region of middle-aged men. Hyaline cell-rich chondroid syringoma is a rare benign variant of chondroid syringoma composed of cells with eosinophilic hyaline cytoplasm and plasmacytoid features, the origin of which remains elusive. Although very few cases have been reported in literature, it is important to be aware of this entity so as to avoid misdiagnosis on histopathological examination. In this report we present a case of hyaline cell-rich chondroid syringoma occurring in the finger.