[Spatial variation in diurnal courses of stem temperature of Betula platyphylla and Fraxinus mandshurica and its influencing factors]

Plant temperature is an important parameter for estimating energy balance and vegetation respiration of forest ecosystem. To examine spatial variation in diurnal courses of stem temperatures (T_s) and its influencing factors, we measured the T_s with copper constantan thermocouples at different depths, heights and azimuths within the stems of two broadleaved tree species with contrasting bark and wood properties, Betula platyphylla and Fraxinus mandshurica. The results showed that the monthly mean diurnal courses of the T_s largely followed that of air temperature with a 'sinusoi dal' pattern, but the T_s lagged behind the air temperature by 0 h at the stem surface to 4 h at 6 cm depth. The daily maximal values and ranges of the diurnal course of T_s decreased gradually with increasing measuring depth across the stem and decreasing measuring height along the stem. The circumferential variation in T_s was marginal, with slightly higher daily maximal values in the south and west directions during the daytime of the dormant season. Differences in thermal properties (i.e. , specific heat capacity and thermal conductivity) of both bark and wood tissue between the two species contributed to the inter specific variations in the radial variation in T_s through influencing the heat exchange between the stem surface and ambient air as well as heat diffusion within the stem. The higher reflectance of the bark of B. platyphylla decreased the influence of solar radiation on T_s. The stepwise regression showed that the diurnal courses of T_s could be well predicted by the environmental factors (R² > 0.85) with an order of influence ranking as air temperature > water vapor pressure > net radiation > wind speed. It is necessary to take the radial, vertical and inter specific varia-tions in T_s into account when estimating biomass heat storage and stem CO2 efflux.

Rapid modulation of ultraviolet shielding in plants is influenced by solar ultraviolet radiation and linked to alterations in flavonoids

The accumulation of ultraviolet (UV)-absorbing compounds (flavonoids and related phenylpropanoids) and the resultant decrease in epidermal UV transmittance (TUV ) are primary protective mechanisms employed by plants against potentially damaging solar UV radiation and are critical components of the overall acclimation response of plants to changing solar UV environments. Whether plants can adjust this UV sunscreen protection in response to rapid changes in UV, as occurs on a diurnal basis, is largely unexplored. Here, we use a combination of approaches to demonstrate that plants can modulate their UV-screening properties within minutes to hours, and these changes are driven, in part, by UV radiation. For the cultivated species Abelmoschus esculentus, large (30-50%) and reversible changes in TUV occurred on a diurnal basis, and these adjustments were associated with changes in the concentrations of whole-leaf UV-absorbing compounds and several quercetin glycosides. Similar results were found for two other species (Vicia faba and Solanum lycopersicum), but no such changes were detected in Zea mays. These findings reveal a much more dynamic UV-protection mechanism than previously recognized, raise important questions concerning the costs and benefits of UV-protection strategies in plants and have practical implications for employing UV to enhance crop vigor and quality in controlled environments.

Herbage intake and ruminal digestion of dairy cows grazed on perennial ryegrass pasture either in the morning or evening

This study aimed to clarify diurnal fluctuations of herbage intake, ruminal fermentation of herbage carbohydrates and proteins, and digesta particulate weight in the rumen of grazing dairy cows. Six ruminally cannulated, non-lactating dairy cows were grazed on perennial ryegrass/white clover pasture either in the morning (04.00 to 08.00 hours) or the evening (16.00 to 20.00 hours). Cows grazed in the evening spent more time (P < 0.01) and consumed more herbage (P < 0.01) compared with cows grazed in the morning. Higher (P < 0.05) daily mean concentrations of total volatile fatty acid, propionate and n-butyrate in rumen fluid were observed for cows grazed in the evening compared with cows grazed in the morning. Although cows grazed in the evening ingested more crude protein compared with cows grazed in the morning, no significant difference in NH3 -N concentration in rumen fluid was observed between them. The ratio of purine-derivative concentration to creatinine concentrations was higher (P < 0.01) in the urine of cows grazed in the evening than in cows grazed in the morning. These results clearly indicated that evening grazing was advantageous for dairy cows compared with morning grazing, in terms of ruminal fermentable energy intake and nitrogen utilization efficiency.

Cardiac autonomic status is associated with spasticity in post-stroke patients

BACKGROUND

Whether post-stroke spasticity is associated with autonomic status is unclear. The purpose of our study was to determine whether spasticity in post-stroke patients is associated with heart rate variability (HRV), an indicator of sympathetic and parasympathetic regulation.

OBJECTIVE

To determine whether HRV is associated with spasticity in post-stroke patients.

METHODS

Our cross-sectional observational study included 21 post-stroke patients with varying degrees of knee spasticity. We measured patients' heart rate variability (HRV) during the morning and afternoon of the same day using the modified Ashworth assessment and the pendulum test. The relationship between HRV and the spasticity parameters was evaluated based on the Pearson correlation coefficient (r).

RESULTS

The data for the morning measurements showed that the relaxation index negatively correlated with the high frequency (HF) power of HRV (r = -0.47, P < 0.05), and positively correlated with the low frequency (LF) power of HRV (r = 0.47, P < 0.05) and the LF/HF power ratio (r = 0.55, P < 0.05). Similar correlations were observed between the diurnal differences of HRV and the relaxation index. No correlation was observed among the data for the afternoon measurements.

CONCLUSIONS

Higher parasympathetic tone and lower sympathetic tone are associated with a higher degree of knee spasticity in post-stroke patients. Further studies are warranted to confirm our findings and investigate the pathological mechanisms involved.

Comparison of the photosynthetic characteristics of four Lycoris species with leaf appearing in autumn under field conditions

The diurnal trends of gas exchange and chlorophyll fluorescence parameters in four Lycoris species (L. houdyshelii, L. aurea, L. radiata var. pumila and L. albiflora) were determined and compared with a portable photosynthesis analysis system. Our study revealed that L. houdyshelii had the lowest light compensation point (LCP), while the other three species had higher LCP (12.37-14.99 μmol m^-2 s^-1); L. aurea had the highest light saturation point (LSP) (1,189 μmol m^-2 s^-1), and L. houdyshelii and L. albiflora had lower LSP with the values being 322 and 345 μmol m^-2 s^-1, respectively, and L. radiata var. pumila showed the intermediate LSP. Both the species L. houdyshelii and L. albiflora exhibited a typical and obvious decline in net photosynthetic rate (P _N) during midday, which was not observed in L. aurea. This indicated a possible photoinhibition in L. houdyshelii and L. albiflora as the ratio of variable to maximum fluorescence (Fv/Fm) values were higher in these two species. The minimal fluorescence (F₀) values were lower in L. aurea and L. radiata var. pumila. The diurnal changes of transpiration rate (E) in all four species presented only one peak, appearing between 11:00 h or 13:00 h. By using simple correlation analyses, it was observed that the environmental factors affecting P _N were different among four species and the main factors were photosynthetic photon flux density (PPFD) and relative humidity especially for L. aurea and L. radiata. The results of studying indicated that the four species could be divided into two groups. The species L. radiata var. pumila and L. aurea were more adapted to a relatively high irradiance, and L. houdyshelii and L. albiflora could be grown in moderate-shade environment in order to scale up their growth and productivity.

Importance of alpha 1-sympathetic activity for diurnal change in ischemic threshold in patients with stable angina

BACKGROUND

Although ischemic threshold reportedly is lower in the early morning than in the afternoon, the mechanisms that account for the diurnal change in minimal coronary vascular resistance in the potentially ischemic area are unknown.

HYPOTHESIS

We hypothesized that calcium-channel blockers and alpha 1 blockers may affect the ischemic threshold in the early morning and afternoon in patients with stable angina.

METHODS

Before and after the administration of the calcium antagonist amlodipine (5 mg) alone and combined with the alpha 1 blocker prazosin (1 mg), a treadmill exercise test using the Balke-Ware protocol was undertaken in the morning (8:00 A.M.) and repeated in the afternoon (1:00 P.M.) with 15 stable angina patients. The ischemic threshold was defined as a reciprocal of minimal coronary vascular resistance in the presence of comparable levels of myocardial ischemia indicated by 0.1 mV ST depression. Minimal coronary vascular resistance was calculated as mean blood pressure divided by coronary blood flow. Since the coronary blood flow is closely related to myocardial oxygen consumption, which can be replaced by the double product of heart rate and systolic blood pressure, minimal coronary vascular resistance was approximated to 1/heart rate.

RESULTS

At baseline, minimal coronary vascular resistance was significantly higher in the early morning than in the afternoon (8.5 +/- 0.3 x 10(-3) min/beats vs. 7.8 +/- 0.4 x 10(-3) min/beats, p < 0.01). Although treatment with amlodipine alone did not abolish the circadian pattern of minimal coronary vascular resistance (8.0 +/- 0.6 x 10(-3) min/beats vs. 7.7 +/- 0.6 x 10(-3) min/ beats, p < 0.05), the addition of prazosin virtually eliminated the diurnal difference in minimal coronary vascular resistance (7.4 +/- 0.5 x 10(-3) min/beats vs. 7.5 +/- 0.5 x 10(-3) min/beats, p = NS).

CONCLUSIONS

These findings indicate that alpha 1-sympathetic activity may play a role in the pathogenesis of the diurnal change of ischemic threshold in patients with stable angina.