Herbarium specimens reveal that mycorrhizal type does not mediate declining temperate tree nitrogen status over a century of environmental change

Rising atmospheric carbon dioxide concentrations (CO2) and atmospheric nitrogen (N) deposition have contrasting effects on ectomycorrhizal (EM) and arbuscular mycorrhizal (AM) symbioses, potentially mediating forest responses to environmental change. In this study, we evaluated the cumulative effects of historical environmental change on N concentrations and δ15N values in AM plants, EM plants, EM fungi, and saprotrophic fungi using herbarium specimens collected in Minnesota, USA from 1871 to 2016. To better understand mycorrhizal mediation of foliar δ15N, we also analyzed a subset of previously published foliar δ15N values from across the United States to parse the effects of N deposition and CO2 rise. Over the last century in Minnesota, N concentrations declined among all groups except saprotrophic fungi. δ15N also declined among all groups of plants and fungi; however, foliar δ15N declined less in EM plants than in AM plants. In the analysis of previously published foliar δ15N values, this slope difference between EM and AM plants was better explained by nitrogen deposition than by CO2 rise. Mycorrhizal type did not explain trajectories of plant N concentrations. Instead, plants and EM fungi exhibited similar declines in N concentrations, consistent with declining forest N status despite moderate levels of N deposition.

Melanization slows the rapid movement of fungal necromass carbon and nitrogen into both bacterial and fungal decomposer communities and soils

Microbial necromass contributes significantly to both soil carbon (C) persistence and ecosystem nitrogen (N) availability, but quantitative estimates of C and N movement from necromass into soils and decomposer communities are lacking. Additionally, while melanin is known to slow fungal necromass decomposition, how it influences microbial C and N acquisition as well as elemental release into soils remains unclear. Here, we tracked decomposition of isotopically labeled low and high melanin fungal necromass and measured 13C and 15N accumulation in surrounding soils and microbial communities over 77 d in a temperate forest in Minnesota, USA. Mass loss was significantly higher from low melanin necromass, corresponding with greater 13C and 15N soil inputs. A taxonomically and functionally diverse array of bacteria and fungi was enriched in 13C and/or 15N at all sampling points, with enrichment being consistently higher on low melanin necromass and earlier in decomposition. Similar patterns of preferential C and N enrichment of many bacterial and fungal genera early in decomposition suggest that both microbial groups co-contribute to the rapid assimilation of resource-rich soil organic matter inputs. While overall richness of taxa enriched in C was higher than in N for both bacteria and fungi, there was a significant positive relationship between C and N in co-enriched taxa. Collectively, our results demonstrate that melanization acts as a key ecological trait mediating not only fungal necromass decomposition rate but also necromass C and N release and that both elements are rapidly co-utilized by diverse bacterial and fungal decomposers in natural settings. IMPORTANCE Recent studies indicate that microbial dead cells, particularly those of fungi, play an important role in long-term carbon persistence in soils. Despite this growing recognition, how the resources within dead fungal cells (also known as fungal necromass) move into decomposer communities and soils are poorly quantified, particularly in studies based in natural environments. In this study, we found that the contribution of fungal necromass to soil carbon and nitrogen availability was slowed by the amount of melanin present in fungal cell walls. Further, despite the overall rapid acquisition of carbon and nitrogen from necromass by a diverse range of both bacteria and fungi, melanization also slowed microbial uptake of both elements. Collectively, our results indicate that melanization acts as a key ecological trait mediating not only fungal necromass decomposition rate, but also necromass carbon and nitrogen release into soil as well as microbial resource acquisition.

The energy cost of horizontal walking and running in adolescents

PURPOSE

This study developed and cross-validated generalized equations for predicting VO2 (mL x kg(-1) x min(-1)) and caloric expenditure (kcal x kg(-1) x min(-1)) during horizontal walking and running in adolescents.

METHODS

Subjects were 47 male and 35 female adolescent volunteers, ages 12-18. Each subject underwent a submaximal treadmill exercise test to determine VO2 at randomly selected walking and jogging speeds (67-215 m x min(-1)). Caloric expenditure was estimated from VO2 and RER. Multiple regression was used to develop prediction equations for estimating VO2 and caloric expenditure from a derivation sample of 77 random observations, both walking and running.

RESULTS

The group relationship between running speed and energy cost in the derivation sample was linear, whereas the relationship between walking speed and energy cost was quadratic. Gender, age, and height each failed to account for significant additional variation in energy cost after speed and mode were considered. Skinfolds accounted for a small yet significant amount of additional variation in energy cost. The derived equations were cross-validated on a sample of 76 separate random observations. The cross-validation statistics are: for VO2, R = 0.95, error = 3.58 mL x kg(-1) x min(-1), and for caloric expenditure, R = 0.94, error = 0.019 kcal x kg(-1) x min(-1). Most selected adult equations consistently underestimated both VO2 and caloric expenditure in the cross-validation sample.

CONCLUSIONS

These results suggest that in adolescents, within the range of speeds tested, the relationship between speed of movement and energy cost for running is linear, but for walking is curvilinear. Also, adult models for estimating VO2 or caloric expenditure do not account for the higher relative energy cost of walking and running in adolescents.

Exercise training does not alter cytochrome P-450 content and microsomal metabolism

The purpose of this investigation was to determine whether increased endurance exercise capacity alters total hepatic cytochrome P-450 content and cytochrome P-450 (CYP1A and CYP2B) mediated hepatic microsomal mixed-function oxidase drug metabolism. Twenty adult male Sprague-Dawley rats were randomly assigned to either a control (C) or an endurance trained group (ET). ET rats were progressively trained 5 d.wk-1 for 11 wk. Both C and ET rats were administered in random order single posttraining doses of probe drugs theophylline (probe for CYP1A) and antipyrine (probe for CYP2B). Soleus muscle citrate synthase activity of ET rats was significantly greater (P < 0.01) than for C rats (mean +/- SD; C, 26.4 +/- 1.3 mumol.g-1.min-1; ET, 46.1 +/- 2.7). In contrast, total liver cytochrome P-450 content was not significantly different (P > 0.01) among C and ET rats (mean +/- SD; C, 0.554 +/- 0.055 nmol.mg-1 liver protein; ET, 0.604 +/- 0.080). Likewise, the posttraining C and ET single-sample plasma clearances of theophylline (mean +/- SD; C, 1.89 +/- 0.360 1.h-1.kg-1 total liver weight; ET, 2.08 +/- 0.49) and antipyrine (mean +/- SD; C, 6.44 +/- 1.56 1.h-1.kg-1 total liver weight; ET, 6.51 +/- 1.02) were not significantly different (P > 0.01). Therefore, it was concluded that strenuous endurance training of 11 wk duration did not alter total hepatic cytochrome P-450 content or CYP1A or CYP2B activity.

Association among fitness components, anxiety, and confidence following aerobic training in aquarunning

The relationship of actual and perceived physiological and physical changes, i.e., VO2max, percent body fat, body weight, and perceived fitness change, to changes in anxiety and confidence were investigated. 15 adults volunteered to participate in an 8-wk. exercise program and 15 adults volunteered to be in a nonexercising control group. Physiological and physical measures (VO2max, percent body fat, body weight) were taken at Week 1 (pretest week) and Week 10 (posttest week) of the program. Each subject completed the Competitive Sport Anxiety Inventory-II prior to and just after the 8-wk. training program. Cognitive and somatic anxiety scores significantly decreased for both groups over the 8-wk. period. Confidence scores did not change for either group. The physiological variable and the physical measures were significantly related to cognitive anxiety, somatic anxiety, or confidence. It appears that both the aquarunning exercise and quiet rest sessions can be associated with anxiety within 8 wk.

Physiological and perceptual responses to walking while swinging hand-held towels

The intent of this investigation was to determine the intensity of cardiovascular exercise produced by walking while swinging hand-held towels and its potential as a training method. Sixteen healthy college students were the volunteer subjects in this experiment. Each subject performed five randomly ordered trials in which they walked with: (1) a normal arm swing (NAS); (2) a vigorous arm swing (VAS); (3) a vigorous arm swing with hand-held towels (VAST); (4) a vigorous arm swing at NAS heart rate (VNH); and (5) a vigorous arm swing with hand-held towels at NAS heart rate (VTNH). Treadmill speed was 89 m.min-1 for VTNH, 103 for VNH, and 119 for NAS, VAS, and VAST trials. Each trial lasted 6 min and was separated by a 2 min walking recovery. Statistical analysis revealed (p < 0.05) that oxygen consumption (VO2), heart rate (HR), and rating of perceived exertion (RPE) were significantly greater for the VAST (27.8 +/- 3.9 ml.kg-1.min-1, 152 +/- 13.8 bpm, 4.2 +/- 1.4 Borg) vs. NAS (21.0 +/- 3.4, 125 +/- 14.7, 2.6 +/- 1.0) and VAS (24.7 +/- 3.7, 139 +/- 14.1, 3.4 +/- 1.1) vs. NAS trials, but were similar for NAS, VNH, and VTNH. Although not statistically significantly different, VO2, HR, and RPE were physiologically greater for the VAST than VAS trial. These results suggest that walking while swinging hand-held towels is a way to: (1) increase oxygen consumption without altering walking speed and (2) slow walking speed yet maintain exercise intensity.

Ground reaction forces in high impact and low impact aerobic dance

The purpose of this study was to compare ground reaction forces (vertical and lateral) produced during commonly used high and low impact aerobic dance maneuvers. Eight experienced aerobic dance instructors were the volunteer subjects. During the first session, three subjects were videotaped performing 10 high and 10 low impact maneuvers that they commonly used in their own class routines. Seven of the high and nine of the low impact maneuvers were then selected and used in sessions 2 and 3. During the second session, all subjects became proficient in performing the chosen maneuvers to music while striking an AMTI force platform with the right foot. During the third session, ground reaction force data generated during footstrike were recorded for each movement. Of the maneuvers examined, 5 high and four low impact maneuvers were used in the data analysis. It was found that maximum vertical active peak and vertical impact peak forces were lower for the low impact maneuvers. Maximum lateral active peak and lateral impact peak forces were similar and highly variable in magnitude for the 2 types of dance. The lower vertical loads produced in low impact dancing may make this type of dance better for minimizing lower extremity overuse injuries in aerobic dance. However, there does not seem to be any advantage in emphasizing the use of low impact dance for minimizing lower extremity injuries that evolve from lateral shear forces.

Resistance exercise effects on plasma cortisol, testosterone and creatine kinase activity in anabolic-androgenic steroid users

Anabolic-androgenic steroids (AS) users have been reported to have an improved ability to withstand exhaustive resistance workouts and to recover more rapidly. The purpose of this investigation was to study the effects of AS usage on the cortisol (C), testosterone (T) and creatine kinase (CK) response to a resistance training session. Eleven trained body builders and power lifters (5.0 +/- 1.6 training years, mean +/- SD), 5 AS users (SU) and 6 nonusers (NU), completed a standardized resistance training session consisting of 10 sets of back squats at preset percentages of the subject's 1 RM max. Blood samples were obtained at rest, immediately post exercise and 24 hours after the exercise session. SU had significantly lower T at rest. Neither group exhibited a significant change in T at 1 min or at 24 h post exercise. Both the NU and SU exhibited a significant increase in CK at 1 min post exercise (129 +/- 23.3 U.l-1, 81 +/- 15.3 U.l-1, respectively), with the NU response significantly greater than the SU. After 24 h, CK for NU was significantly elevated (171.9 +/- 54.5 U.l-1) above resting level. In contrast, CK for SU had returned to resting level. NU had a significant increase in cortisol (C) (p less than 0.05) at 1 min post exercise (156.8 +/- 10.9 nmol.l-1), while the SU cortisol was not significantly changed. By 24 h C for the NU returned to resting level. The results of this investigation support the concept that AS users have a diminished CK response and an altered stress response to a single bout of resistance exercise.

Effects of 4- and 8-h preexercise feedings on substrate use and performance

Seven well-trained male cyclists were studied during 105 min of cycling (65% of maximal oxygen uptake) and a 15-min "performance ride" to compare the effects of 4- and 8-h preexercise carbohydrate (CHO) feedings on substrate use and performance. A high CHO meal was given 1) 4-h preexercise (M-4), 2) 8-h preexercise (M-8), 3) 4-h preexercise with CHO feedings during exercise (M-4CHO), and 4) 8-h preexercise with CHO feedings during exercise (M-8CHO). Blood samples were obtained at 0, 15, 60, 105, and 120 min and analyzed for lactate, glucose, insulin, and glycerol. Total work output during the performance ride was similar for the M-4 (217,893 +/- 13,348 N/m) and M-8 trials (216,542 +/- 13,905) and was somewhat higher for the M-4CHO (223,994 +/- 14,387) and M-8CHO (224,702 +/- 15,709) trials (P = 0.059, NS). Glucose was significantly elevated throughout exercise, and insulin levels were significantly elevated at 15 and 60 min during M-4CHO and M-8CHO compared with M-4 and M-8 trials. Glycerol levels were significantly lower during the CHO feeding trials compared with placebo and were not significantly different during exercise when the subject had fasted an additional 4 h. The results of this study suggest that when preexercise meals are ingested 4 or 8 h before submaximal cycling exercise, substrate use and performance are similar.