Subscriber access provided by READING UNIV
Article
Assessing Cumulative Effects of Climate Change Manipulations on Phosphorous Limitation in a Californian Grassland. Travis Mellett, Corinne Selvin, Delphine Defforey, Kathryn Roberts, Alanna Lecher, Kate J. Dennis, Jessica Gutknecht, Christopher Field, and Adina Paytan Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b04362 • Publication Date (Web): 01 Dec 2017 Downloaded from http://pubs.acs.org on December 2, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 30
Environmental Science & Technology
Assessing Cumulative Effects of Climate Change Manipulations on Phosphorus Limitation in a Californian Grassland. Travis Mellett1^ , Corinne Selvin1, Delphine Defforey1, Kathryn Roberts2, Alanna L. Lecher3, Kate Dennis4, Jessica Gutknecht5, Christopher Field6, Adina Paytan2* 1
Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA, 95064
2
Institute of Marine Sciences, University of California Santa Cruz, Santa Cruz, CA, 95064 3
Natural and Applied Sciences, Lynn University, Boca Raton, FL, 33431 4
5
6
Picarro Inc., 3105 Patrick Henry Drive, Santa Clara, CA, 95054
Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN, 55108
Department of Global Ecology, Carnegie Institution of Washington, Stanford, CA 94305 * corresponding author:
[email protected], phone 831-459-1437
^ present address: College of Marine Science, University of South Florida, Saint Petersburg, Fl, 33701
ACS Paragon Plus Environment 1
Environmental Science & Technology
Page 2 of 30
KEYWORDS: Phosphate, Biogeochemistry, Grasslands, Climate Change
1
ABSTRACT
2
Grasslands throughout the world are responding in diverse ways to changing climate and
3
environmental conditions. In this study we analyze indicators of phosphorus limitation including
4
phosphorus concentrations, phosphorus to nitrogen and carbon ratios, oxygen isotope ratios of
5
phosphate in vegetation, and phosphatase enzyme activity in soil to shed light on potential
6
effects of climate change on phosphorus availability to grassland vegetation. The study was
7
conducted at the Jasper Ridge Global Change Experiment, (JRGCE) California where
8
manipulations mimicking increases in temperature, water, nitrogen and carbon-dioxide have
9
been maintained for over 15 years. We compare our results to an earlier study conducted 3 years
10
after the start of the experiment, in order to assess any change in the response of phosphorus over
11
time. Our results suggest that a decade later the measured indicators show similar or only slightly
12
stronger responses. Specifically, addition of nitrogen, the principle parameter controlling
13
biomass growth, increased phosphorus demand but thresholds that suggest P limitation were not
14
reached. A study documenting changes in net primary productivity (NPP) over time at the
15
JRGCE also could not identify a progressive effect of the manipulations on NPP. Combined
16
these results indicate that the vegetation in these grassland systems is not very sensitive to the
17
range of climate parameters tested.
18 19
1.0 Introduction
ACS Paragon Plus Environment 2
Page 3 of 30
Environmental Science & Technology
20
Phosphorus (P) is an essential macronutrient for life and a major component of plants. It
21
plays a critical role in the structure of DNA, RNA, and cell membranes as well as in transmission
22
of energy in the form of ATP 1. The abundance and availability of P in soil has the capacity to
23
limit the growth of plants, and thus to affect food supply, plant productivity, and ecosystem
24
structure and function 2. In many ecosystems, the essential nutrients nitrogen (N) and/or P
25
constrain growth 3-5. It has been suggested that the influence of anthropogenic global change and
26
specifically the increase in atmospheric N deposition may push more systems towards P limited
27
conditions
28
productivity of many grassland systems worldwide
29
primary productivity, including temperature, water availability, day length, along with other
30
environmental parameters; and actual responses to each environmental variable or combination
31
of variables are difficult to predict 6. This underscores the importance of experimental
32
investigation in understanding the impacts global change will have on terrestrial environments,
33
including their response to anthropogenic perturbations and specifically how P dynamics may be
34
impacted by such changes.
4-9
. Recent work has highlighted the role of N and P, and other nutrients in limiting 4, 5, 9
. However other factors can affect
35
The JRGCE is a long-term study on the effects of expected climate and anthropogenic
36
changes on California grasslands. The experiment is designed to test the effects of increased bio-
37
available N, carbon dioxide (CO2), temperature, and precipitation and all combinations of these
38
effects on the ecology and biogeochemical cycles in this ecosystem
39
incorporates eight iterations of each of the four amendment combinations resulting in 16 unique
40
treatments and 128 total treatment plots. A study on P biogeochemistry at the site by Menge and
41
Field
42
treatments where N was added plants exhibited signs of P limitation. We note that the term P
7
10, 11
. The study site
which was conducted three years after the start of the experiment concluded that in
ACS Paragon Plus Environment 3
Environmental Science & Technology
Page 4 of 30
43
limitation used in that study as in many other studies including this one does not necessarily
44
imply that NPP is reduced but rather that the biologically available inorganic P is lower than the
45
plants’ demand, resulting in physiological changes such as production of enzymes to acquire
46
other P forms or changes in cellular P quotas. Six indices of P limitation were used to evaluate
47
treatment impacts: soil phosphatase activity, P concentration and N:P ratios in green and in
48
senescent leaves of the dominant grass genus, Avena and the total aboveground plant P content.
49
They found that all indices indicated that N deposition, the only factor that stimulated NPP (by a
50
factor of 23% relative to control
51
temperature and water supply), did not stimulate NPP or an increase in P demand by the
52
vegetation. A more recent analysis of changes in NPP response to the climate manipulations over
53
the 15 years of the JRGCE suggested that given the interacting effects of predicted climate
54
change conditions, future conditions will likely result in lower NPP (albeit with large interannual
55
variability) 12. The current study reported here was also conducted 15 years after the start of the
56
experiment and 12 years after the study of P indicators by Menge and Fields 7, in order to
57
determine if any further progression or decrease in P limitation conditions has occurred and how
58
this may inform other trends observed at the JRGCE.
12
), increased P demand. The other three factors (CO2,
59
We use some of the same indices employed by the previous study: total P concentrations
60
and N:P ratios of the bulk aboveground biomass and of green A. barbata, and soil alkaline
61
phosphatase activity to evaluate changes in these indices over time. We also use C and N
62
concentrations, C:N and C:P ratios of A. barbata, and of the bulk homogenized aboveground
63
biomass, as well as the soil enzyme activities of acid, alkaline, and neutral phosphatases, and
64
β−Glucosidase to gain additional information of the nutrient dynamics in this ecosystem. It is
65
expected that as P becomes less available P content the plants will decrease as less luxury uptake
ACS Paragon Plus Environment 4
Page 5 of 30
Environmental Science & Technology
66
and storage will be possible. If N is not depleted then this will also result in higher N:P and C:P
67
ratios in plant tissue. Under such condition plants (and bacteria) will produce phosphatase
68
enzymes that hydrolyze organic P compounds to increase phosphate availability hence an
69
increase in the activity of phosphatase enzymes suggests that there is not enough phosphate to
70
satisfy growth. In addition to these measurements, the oxygen isotope ratio of phosphate (δ18OP)
71
in A. barbata was measured to evaluate if P limitation affects this ratio in living plant leaves.
72
δ18OP has not been previously tested as an indicator of P limitation; we hypothesized that when P
73
is scarce cellular P will be extensively cycled resulting in isotopic equilibrium
74
when available may be stored as polyphosphate which might not be cycled and equilibrated with
75
plant cellular water. This suite of analyses was used to shed light on P cycling and allocation,
76
and changes in the extent of P limitation (e.g. availability vs demand) since the previous study of
77
Menge and Field 7 and how this relates to trends in NPP at JRGCE.
13
while excess P
78 79
2.0 Methods
80
2.1 Study Site and Experimental Design
81
Jasper Ridge Biological Preserve is located in the San Francisco Bay area (37°24’N,
82
122°14’W). The site experiences a Mediterranean-type climate, with cool, wet winters and hot,
83
dry summers. The soil at the site is a fine grain, mixed Typic Haploxeralf derived from either
84
sandstone or greenstone from the Franciscan complex with a pH ranging from 6.5 and 7 14. The
85
plant community at the site is dominated by introduced forbs (primarily Geranium dissectum and
86
Erodium botrys) and grasses (Avena barbata, Avena fatua, Bromus hordeaceus, Lolium
87
multiflorum, and Bromus diadrus) with few native species 11.
ACS Paragon Plus Environment 5
Environmental Science & Technology
Page 6 of 30
88
The four parameters chosen for manipulation in this climate study are atmospheric CO2
89
(CO2), temperature (H), precipitation (W), and nitrate deposition (N). Atmospheric CO2 is
90
elevated by +275 µmol·mol-1. Temperature is increased by +80 to +250W·m-2 (corresponding to
91
1-1.5 °C above ambient), precipitation is elevated to 150% ambient values, and N deposition is
92
increased by adding 7g NO3- m-2 yr-1 (as a 2 g pulse as liquid Ca(NO3)2 with the first autumn
93
rains and 5 g as a time-release pellet application (Osmocote) in January of each year) in addition
94
to the background rate of
