The role of internal and external nitrogen pools in bermudagrass growth during spring emergence from dormancy

As bermudagrass (Cynodon dactylon (L.) Pers.) transitions from winter dormancy to active growth in spring, nitrogen is essential for new tissue growth. We examined the relative contributions of internally stored nitrogen and that taken up by preexisting and newly produced roots. Field-collected dormant bermudagrass was transferred to a nutrient solution culture system in a growth chamber. Cultures were provided either a non-nitrogen-containing solution or one amended with nitrate labeled with the ¹⁵N isotope of nitrogen, which allowed tracking of endogenous and exogenous N pools in all tissues as growth began. Nitrogen in stolon internodes was the largest N source for early growth. Though mass increased at the same rate in both N treatments over 3 weeks of growth, the unfertilized treatment showed early signs of nitrogen deficiency: low tissue N, slowed leaf elongation, and fewer but longer roots. Preexisting roots were active in absorption almost immediately; new roots were produced quickly and had even higher N uptake rates.     

A minimal model of the variability of marine ecosystems

In marine ecology, population abundance time series often reveal patterns, such as decadal pseudo-cycles, on scales that make them difficult to mathematically characterize by means of conventional models based on functional responses. We propose here a simple non-deterministic model based on three strong ecological constraints, without any use of functional responses or external factors: (i) mass balance constraints between flows and biomass, (ii) a satiation constraint relating inflows and biomass and (iii) an inertia principle restricting the variation of populations of a given species according to its lifespan. This model reproduces in a robust manner observed patterns of variability and can be used to question the relevance of other modelling approaches of ecosystem dynamics with regard to determinism, constraints and stochasticity. Referring to a non-deterministic model without any functional relationships and environmental or anthropogenic forcing can help in avoiding misleading advice based on the belief that we can explain the causes of observed patterns, which may simply result from basic structural constraints within which the ecosystem functions.     

Clinical outcomes in cats with renal carcinoma undergoing nephrectomy: A retrospective study

Renal carcinomas (RC) are uncommonly encountered in feline medicine. Limited information regarding clinical presentation and postoperative outcomes is available. The purpose of this multi-institutional, retrospective study was to describe the presenting features and clinical outcomes of cats with RC undergoing nephrectomy. Thirty-six client-owned cats were included. Medical records from participating institutions were searched to identify cats that had a histopathologic diagnosis of RC and underwent nephrectomy from January 2001 to October 2021. The most common presenting complaints were weight loss (36.1%) and hyporexia (30.6%). Based on preoperative imaging and intraoperative findings, eight cats had suspected metastasis at the time of surgery (22.2%). Twenty-eight cats survived to discharge (77.8%). Median progression free interval (PFI) could not be determined, as only six cats developed suspected recurrence (16.7%) and seven cats developed suspected metastasis (19.4%). The all-cause median survival time (MST) was 203 days (95% confidence interval [CI]: 84, 1379 days). When cases that died prior to discharge were excluded, MST increased to 1217 days (95% CI: 127, 1641 days). One-year, two-year, and three-year survival rates were all 40.4%. Neither renal tumour histologic subtype nor the presence of preoperative azotemia, anaemia, erythrocytosis, haematuria, or suspected metastasis at diagnosis were found to influence survival. For cats surviving to discharge, prolonged survival times were possible. Further studies are necessary to elucidate other potential prognostic factors, the utility of postoperative adjuvant treatment, and to identify cats at-risk of mortality in the perioperative period.